[3.12] gh-89363: Skip threading test_is_alive_after_fork() if ASAN (GH-109835) (#109855)

gh-89363: Skip threading test_is_alive_after_fork() if ASAN (GH-109835)

Skip test_is_alive_after_fork() of test_threading if Python is built
with Address Sanitizer (ASAN).
(cherry picked from commit bc06743533b5fea2d5ecdad6dd3caa372c67439f)

Co-authored-by: Victor Stinner <vstinner@python.org>