Applying move_only_holder_caster_sfinae.patch (copybara cannot handle the combination).

include/pybind11/cast.h

@@ -2260,7 +2260,7 @@ template <typename T>
 class type_caster<std::shared_ptr<T>> : public copyable_holder_caster<T, std::shared_ptr<T>> { };
 #endif
 
-template <typename type, typename holder_type>
+template <typename type, typename holder_type, typename SFINAE = void>
 struct move_only_holder_caster {
     static_assert(std::is_base_of<type_caster_base<type>, type_caster<type>>::value,
             "Holder classes are only supported for custom types");