Build errors in pybind11_protobuf with Protobuf 35.1

**What version of OR-Tools and what language are you using?**

https://github.com/google/or-tools/commit/98c165af62df62b3056c2ee0fca66b24e79097cb
GCC 15.2.1
probotuf 35.1
pybind 2.13.6 (if used)
Python 3.10

CMake options:
```sh
-DBUILD_SHARED_LIBS=TRUE \
-DCMAKE_CXX_STANDARD=17 \
-DBUILD_CXX=ON \
-DCMAKE_CXX_FLAGS="-Wno-format-security" \
-DBUILD_CXX_EXAMPLES=OFF \
-DBUILD_CXX_SAMPLES=OFF \
-DBUILD_DOTNET=OFF \
-DBUILD_JAVA=OFF \
-DBUILD_PYTHON=ON \
-DBUILD_SAMPLES=OFF \
-DBUILD_DEPS=OFF \
-DBUILD_pybind11_abseil=ON \
-DBUILD_pybind11_protobuf=ON \
-DUSE_CPLEX=OFF \
-DUSE_COINOR=ON \
-DUSE_GLPK=ON \
-DUSE_HIGHS=OFF \
-DUSE_SCIP=ON \
-DUSE_SYSTEM_ABSEIL=ON \
-DUSE_SYSTEM_PROTOBUF=ON \
-DUSE_SYSTEM_PYBIND=ON \
-DVENV_USE_SYSTEM_SITE_PACKAGES=ON \
-DGENERATE_PYTHON_STUB=OFF \
-Wno-dev
```
leads to:
```
./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:358:10: error: 'bool pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase::FindFileByName(const std::string&, google::protobuf::FileDescriptorProto*)' marked 'override', but does not override
358 | bool FindFileByName(const std::string& filename,
| ^~~~~~~~~~~~~~
./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:374:10: error: 'bool pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase::FindFileContainingSymbol(const std::string&, google::protobuf::FileDescriptorProto*)' marked 'override', but does not override
374 | bool FindFileContainingSymbol(const std::string& symbol_name,
| ^~~~~~~~~~~~~~~~~~~~~~~~
./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:392:10: error: 'bool pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase::FindFileContainingExtension(const std::string&, int, google::protobuf::FileDescriptorProto*)' marked 'override', but does not override
392 | bool FindFileContainingExtension(const std::string& containing_type,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/15.2.1/memory:80,
from /usr/include/pybind11/detail/common.h:318,
from /usr/include/pybind11/attr.h:13,
from /usr/include/pybind11/detail/class.h:12,
from /usr/include/pybind11/pybind11.h:13,
from ./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.h:6,
from ./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:1:
/usr/include/c++/15.2.1/bits/unique_ptr.h: In instantiation of 'std::__detail::__unique_ptr_t<_Tp> std::make_unique(_Args&& ...) [with _Tp = pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase; _Args = {pybind11::object}; __detail::__unique_ptr_t<_Tp> = __detail::__unique_ptr_t]':
./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:319:62: required from here
319 | auto database = absl::make_unique(
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
320 | py::reinterpret_borrow(python_pool));
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/15.2.1/bits/unique_ptr.h:1084:30: error: invalid new-expression of abstract class type 'pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase'
1084 | { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:349:9: note: because the following virtual functions are pure within 'pybind11_protobuf::{anonymous}::PythonDescriptorPoolWrapper::DescriptorPoolDatabase':
349 | class DescriptorPoolDatabase : public DescriptorDatabase {
| ^~~~~~~~~~~~~~~~~~~~~~
In file included from ./build/_deps/pybind11_protobuf-src/pybind11_protobuf/proto_cast_util.cc:27:
/usr/include/google/protobuf/descriptor_database.h:67:52: note: 'virtual bool google::protobuf::DescriptorDatabase::FindFileByName(std::string_view, google::protobuf::FileDescriptorProto*)'
67 | PROTOBUF_FUTURE_ADD_EARLY_NODISCARD virtual bool FindFileByName(
| ^~~~~~~~~~~~~~
/usr/include/google/protobuf/descriptor_database.h:74:52: note: 'virtual bool google::protobuf::DescriptorDatabase::FindFileContainingSymbol(std::string_view, google::protobuf::FileDescriptorProto*)'
74 | PROTOBUF_FUTURE_ADD_EARLY_NODISCARD virtual bool FindFileContainingSymbol(
| ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/google/protobuf/descriptor_database.h:82:52: note: 'virtual bool google::protobuf::DescriptorDatabase::FindFileContainingExtension(std::string_view, int, google::protobuf::FileDescriptorProto*)'
82 | PROTOBUF_FUTURE_ADD_EARLY_NODISCARD virtual bool FindFileContainingExtension(
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Using instead

` -DBUILD_pybind11_protobuf=OFF \`

leads to
```
CMake Error at cmake/system_deps.cmake:128 (find_package):
By not providing "Findpybind11_protobuf.cmake" in CMAKE_MODULE_PATH this
project has asked CMake to find a package configuration file provided by
"pybind11_protobuf", but CMake did not find one.

Could not find a package configuration file provided by "pybind11_protobuf"
with any of the following names:

pybind11_protobufConfig.cmake
pybind11_protobuf-config.cmake
[..]
```