* Add tests only. Fails to build with this error message:

```
g++ -o pybind11/tests/test_copy_move.os -c -std=c++17 -fPIC -fvisibility=hidden -O0 -g -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -Wundef -Wnon-virtual-dtor -Wunused-result -Werror -isystem /usr/include/python3.11 -isystem /usr/include/eigen3 -DPYBIND11_STRICT_ASSERTS_CLASS_HOLDER_VS_TYPE_CASTER_MIX -DPYBIND11_ENABLE_TYPE_CASTER_ODR_GUARD_IF_AVAILABLE -DPYBIND11_TEST_BOOST -DPYBIND11_INTERNALS_VERSION=10000000 -Ipybind11/include -I/usr/local/google/home/rwgk/forked/pybind11/include -I/usr/local/google/home/rwgk/clone/pybind11/include /usr/local/google/home/rwgk/forked/pybind11/tests/test_copy_move.cpp
In file included from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../cast.h:15,
                 from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../attr.h:14,
                 from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/class.h:12,
                 from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/pybind11.h:13,
                 from /usr/local/google/home/rwgk/forked/pybind11/include/pybind11/stl.h:12,
                 from /usr/local/google/home/rwgk/forked/pybind11/tests/test_copy_move.cpp:11:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h: In instantiation of ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(const itype&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../cast.h:1230:37:   required from ‘pybind11::object pybind11::cast(T&&, return_value_policy, handle) [with T = const UnusualOpRef&; typename std::enable_if<(! std::is_base_of<detail::pyobject_tag, typename std::remove_reference<_Tp>::type>::value), int>::type <anonymous> = 0]’
/usr/local/google/home/rwgk/forked/pybind11/tests/test_copy_move.cpp:162:80:   required from here
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1110:20: error: no matching function for call to ‘pybind11::detail::type_caster_base<UnusualOpRef>::cast(const UnusualOpRef::NonTrivialType, pybind11::return_value_policy&, pybind11::handle&)’
 1110 |         return cast(&src, policy, parent);
      |                ~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1105:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(const itype&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1105 |     static handle cast(const itype &src, return_value_policy policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1105:37: note:   no known conversion for argument 1 from ‘const UnusualOpRef::NonTrivialType’ {aka ‘const std::shared_ptr<int>’} to ‘const pybind11::detail::type_caster_base<UnusualOpRef>::itype&’ {aka ‘const UnusualOpRef&’}
 1105 |     static handle cast(const itype &src, return_value_policy policy, handle parent) {
      |                        ~~~~~~~~~~~~~^~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1113:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(itype&&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1113 |     static handle cast(itype &&src, return_value_policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1113:32: note:   no known conversion for argument 1 from ‘const UnusualOpRef::NonTrivialType’ {aka ‘const std::shared_ptr<int>’} to ‘pybind11::detail::type_caster_base<UnusualOpRef>::itype&&’ {aka ‘UnusualOpRef&&’}
 1113 |     static handle cast(itype &&src, return_value_policy, handle parent) {
      |                        ~~~~~~~~^~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1142:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(const itype*, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1142 |     static handle cast(const itype *src, return_value_policy policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1142:37: note:   no known conversion for argument 1 from ‘const UnusualOpRef::NonTrivialType’ {aka ‘const std::shared_ptr<int>’} to ‘const pybind11::detail::type_caster_base<UnusualOpRef>::itype*’ {aka ‘const UnusualOpRef*’}
 1142 |     static handle cast(const itype *src, return_value_policy policy, handle parent) {
      |                        ~~~~~~~~~~~~~^~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h: In instantiation of ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(itype&&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’:
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../cast.h:1230:37:   required from ‘pybind11::object pybind11::cast(T&&, return_value_policy, handle) [with T = UnusualOpRef; typename std::enable_if<(! std::is_base_of<detail::pyobject_tag, typename std::remove_reference<_Tp>::type>::value), int>::type <anonymous> = 0]’
/usr/local/google/home/rwgk/forked/pybind11/tests/test_copy_move.cpp:163:74:   required from here
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1114:20: error: no matching function for call to ‘pybind11::detail::type_caster_base<UnusualOpRef>::cast(UnusualOpRef::NonTrivialType, pybind11::return_value_policy, pybind11::handle&)’
 1114 |         return cast(&src, return_value_policy::move, parent);
      |                ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1105:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(const itype&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1105 |     static handle cast(const itype &src, return_value_policy policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1105:37: note:   no known conversion for argument 1 from ‘UnusualOpRef::NonTrivialType’ {aka ‘std::shared_ptr<int>’} to ‘const pybind11::detail::type_caster_base<UnusualOpRef>::itype&’ {aka ‘const UnusualOpRef&’}
 1105 |     static handle cast(const itype &src, return_value_policy policy, handle parent) {
      |                        ~~~~~~~~~~~~~^~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1113:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(itype&&, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1113 |     static handle cast(itype &&src, return_value_policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1113:32: note:   no known conversion for argument 1 from ‘UnusualOpRef::NonTrivialType’ {aka ‘std::shared_ptr<int>’} to ‘pybind11::detail::type_caster_base<UnusualOpRef>::itype&&’ {aka ‘UnusualOpRef&&’}
 1113 |     static handle cast(itype &&src, return_value_policy, handle parent) {
      |                        ~~~~~~~~^~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1142:19: note: candidate: ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast(const itype*, pybind11::return_value_policy, pybind11::handle) [with type = UnusualOpRef; itype = UnusualOpRef]’
 1142 |     static handle cast(const itype *src, return_value_policy policy, handle parent) {
      |                   ^~~~
/usr/local/google/home/rwgk/forked/pybind11/include/pybind11/detail/../detail/type_caster_base.h:1142:37: note:   no known conversion for argument 1 from ‘UnusualOpRef::NonTrivialType’ {aka ‘std::shared_ptr<int>’} to ‘const pybind11::detail::type_caster_base<UnusualOpRef>::itype*’ {aka ‘const UnusualOpRef*’}
 1142 |     static handle cast(const itype *src, return_value_policy policy, handle parent) {
      |                        ~~~~~~~~~~~~~^~~
```

* Replace `&src` with `std::addressof(src)` to fix the error building the added tests.

* Fix accident (not sure how the `const` slipped in here when transferring the diff from pybind11k).