[3.12] gh-110017: Disable test_signal.test_stress_modifying_handlers on macOS (GH-112834) (#112851)

gh-110017: Disable test_signal.test_stress_modifying_handlers on macOS (GH-112834)

Test test_stress_modifying_handlers in test_signal can crash
the interpreter due to a bug in macOS. Filed as FB13453490
with Apple.
(cherry picked from commit bf0beae6a05f3266606a21e22a4d803abbb8d731)

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>