gh-105922: Use PyImport_AddModuleRef() function

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Replace PyImport_AddModuleObject() + Py_XNewRef() with PyImport_AddModuleRef() to get directly a strong reference.

• Issue: C API: Add PyImport_AddModuleRef() function #105922

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test_threading failed with a warning on the Address sanitizer CI:

test_4_daemon_threads (test.test_threading.ThreadJoinOnShutdown.test_4_daemon_threads) ... ok
test_clear_threads_states_after_fork (test.test_threading.ThreadJoinOnShutdown.test_clear_threads_states_after_fork) ... ok
test_reinit_tls_after_fork (test.test_threading.ThreadJoinOnShutdown.test_reinit_tls_after_fork) ... Warning -- Uncaught thread exception: AssertionError
Exception in thread Thread-36 (do_fork_and_wait):
Traceback (most recent call last):
File "/home/runner/work/cpython/cpython/Lib/threading.py", line 1052, in _bootstrap_inner
self.run()
File "/home/runner/work/cpython/cpython/Lib/threading.py", line 989, in run
self._target(*self._args, **self._kwargs)
File "/home/runner/work/cpython/cpython/Lib/test/test_threading.py", line 1173, in do_fork_and_wait
support.wait_process(pid, exitcode=50)
File "/home/runner/work/cpython/cpython/Lib/test/support/__init__.py", line 2156, in wait_process
raise AssertionError(f"process {pid} is still running "
AssertionError: process 21364 is still running after 300.3 seconds
ok