When reloading_datetime module, the single-phase version did not invoke thePyInit__datetime function, whereas the current multi-phase version updates the static types through the module init. The outdated static type cache in the interpreter state needs to be invalidated at the end of reloading the multi-phase module.

This PR is a manual backport ofa81d434, addingassert statements to the test case.
This also backportse6076d1 (gh-120180) manually.

• Issue:test_datetime fails with a--forever argument #120782