pythongh-117657: Skip tests that use threads after fork (python#122194)

These tests fail when run under thread sanitizer due to the use of fork
and threads.

Lib/test/test_asyncio/test_unix_events.py

@@ -1212,6 +1212,7 @@ async def test_fork_not_share_event_loop(self):
             wait_process(pid, exitcode=0)
 
     @hashlib_helper.requires_hashdigest('md5')
+    @support.skip_if_sanitizer("TSAN doesn't support threads after fork", thread=True)
     def test_fork_signal_handling(self):
         self.addCleanup(multiprocessing_cleanup_tests)
 
@@ -1258,6 +1259,7 @@ async def func():
         self.assertTrue(child_handled.is_set())
 
     @hashlib_helper.requires_hashdigest('md5')
+    @support.skip_if_sanitizer("TSAN doesn't support threads after fork", thread=True)
     def test_fork_asyncio_run(self):
         self.addCleanup(multiprocessing_cleanup_tests)
 
@@ -1277,6 +1279,7 @@ async def child_main():
         self.assertEqual(result.value, 42)
 
     @hashlib_helper.requires_hashdigest('md5')
+    @support.skip_if_sanitizer("TSAN doesn't support threads after fork", thread=True)
     def test_fork_asyncio_subprocess(self):
         self.addCleanup(multiprocessing_cleanup_tests)