gh-121065: Temporarily skip flaky test on free-threaded build (#121100)

Author: colesbury

Lib/test/test_signal.py

@@ -1345,6 +1345,7 @@ def handler(signum, frame):
         # Python handler
         self.assertEqual(len(sigs), N, "Some signals were lost")
 
+    @support.requires_gil_enabled("gh-121065: test is flaky on free-threaded build")
     @unittest.skipIf(is_apple, "crashes due to system bug (FB13453490)")
     @unittest.skipUnless(hasattr(signal, "SIGUSR1"),
                          "test needs SIGUSR1")