Use newer PyCode API and other fixes (#4916)

* Use PyCode API

* style: pre-commit fixes

* Free locals

* Fix PY_VERSION_HEX check

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/pybind11/pybind11.h

@@ -2751,10 +2751,15 @@ get_type_override(const void *this_ptr, const type_info *this_type, const char *
         if ((std::string) str(f_code->co_name) == name && f_code->co_argcount > 0) {
         if ((std::string) str(f_code->co_name) == name && f_code->co_argcount > 0) {
             PyObject *locals = PyEval_GetLocals();
             PyObject *locals = PyEval_GetLocals();
             if (locals != nullptr) {
             if (locals != nullptr) {
+#        if PY_VERSION_HEX >= 0x030b0000
+                PyObject *co_varnames = PyCode_GetVarnames(f_code);
+#        else
                 PyObject *co_varnames = PyObject_GetAttrString((PyObject *) f_code, "co_varnames");
                 PyObject *co_varnames = PyObject_GetAttrString((PyObject *) f_code, "co_varnames");
+#        endif
                 PyObject *self_arg = PyTuple_GET_ITEM(co_varnames, 0);
                 PyObject *self_arg = PyTuple_GET_ITEM(co_varnames, 0);
                 Py_DECREF(co_varnames);
                 Py_DECREF(co_varnames);
                 PyObject *self_caller = dict_getitem(locals, self_arg);
                 PyObject *self_caller = dict_getitem(locals, self_arg);
+                Py_DECREF(locals);
                 if (self_caller == self.ptr()) {
                 if (self_caller == self.ptr()) {
                     Py_DECREF(f_code);
                     Py_DECREF(f_code);
                     Py_DECREF(frame);
                     Py_DECREF(frame);