`test_shutdown_default_executor_timeout` asyncio test is flaky

[colesbury]

Bug report

Seen in https://github.com/python/cpython/actions/runs/13606907022/job/38039459160?pr=130732

FAIL: test_shutdown_default_executor_timeout (test.test_asyncio.test_base_events.BaseEventLoopTests.test_shutdown_default_executor_timeout)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\test_asyncio\test_base_events.py", line 246, in test_shutdown_default_executor_timeout
    with self.assertWarnsRegex(RuntimeWarning,
         ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
                               "The executor did not finishing joining"):
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: RuntimeWarning not triggered

Linked PRs

• gh-130736: Fix asyncio test_shutdown_default_executor_timeout() #130800
• [3.13] gh-130736: Fix asyncio test_shutdown_default_executor_timeout() (GH-130800) #130825
• [3.12] gh-130736: Fix asyncio test_shutdown_default_executor_timeout() (GH-130800) #130826

[picnixz]

(I've added the free-threading label because I think it's easier to remove it rather than add it)

[vstinner]

I wrote PR #130800 to fix the test.