Bug fix: Replace bare `static exception<T>` with `gil_safe_call_once_and_store`. (#4897)

This is to ensure that `Py_DECREF()` is not called after the Python interpreter was finalized already:

https://github.com/pybind/pybind11/blob/3414c56b6c7c521d868c9a137ca2ace2e26b5b2e/include/pybind11/gil_safe_call_once.h#L19