pythongh-118433: Temporarily skip test_interrupt_main_subthread in free-threaded builds (python#118485)

Free-threaded builds can intermittently tickle a longstanding bug (24 years!)
in the implementation of `threading.Condition`, leading to flakiness in the
test suite. Fixing the underlying issue will require more discussion, and will
likely apply to most of the concurrency primitives in the `threading` module
that are written in Python. See pythongh-118433 for more details.

Author: mpage

Lib/test/test_threading.py

@@ -3,7 +3,7 @@
 """
 
 import test.support
-from test.support import threading_helper, requires_subprocess
+from test.support import threading_helper, requires_subprocess, requires_gil_enabled
 from test.support import verbose, cpython_only, os_helper
 from test.support.import_helper import import_module
 from test.support.script_helper import assert_python_ok, assert_python_failure
@@ -2025,6 +2025,7 @@ def check_interrupt_main_noerror(self, signum):
             # Restore original handler
             signal.signal(signum, handler)
 
+    @requires_gil_enabled("gh-118433: Flaky due to a longstanding bug")
     def test_interrupt_main_subthread(self):
         # Calling start_new_thread with a function that executes interrupt_main
         # should raise KeyboardInterrupt upon completion.