test_staggered_race_with_eager_tasks fails with CancelledError

[rossburton]

Bug report

Bug description:

We're occasionally seeing test.test_asyncio.test_eager_task_factory.PyEagerTaskFactoryLoopTests.test_staggered_race_with_eager_tasks fail:

Traceback (most recent call last):
  File "/usr/lib/python3.14/test/test_asyncio/test_eager_task_factory.py", line 242, in test_staggered_race_with_eager_tasks
    self.run_coro(run())
    ~~~~~~~~~~~~~^^^^^^^
  File "/usr/lib/python3.14/test/test_asyncio/test_eager_task_factory.py", line 36, in run_coro
    return self.loop.run_until_complete(coro)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/usr/lib/python3.14/asyncio/base_events.py", line 720, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/usr/lib/python3.14/asyncio/futures.py", line 208, in result
    raise self._exception.with_traceback(self._exception_tb)
  File "/usr/lib/python3.14/asyncio/tasks.py", line 289, in __step_run_and_handle_result
    result = coro.send(None)
  File "/usr/lib/python3.14/test/test_asyncio/test_eager_task_factory.py", line 240, in run
    self.assertIsInstance(excs[2], ValueError)
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
AssertionError: CancelledError() is not an instance of <class 'ValueError'>

This is rarely happening, but we've seen it in CI runs of the Python test suite (OpenEmbedded, Python 3.14.7).

CPython versions tested on:

3.14

Operating systems tested on:

Linux