twisted.python.test.test_sendmsg.SendmsgTests.test_sendSubProcessFD is flaky

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https://github.com/twisted/twisted/actions/runs/8942946452/job/24566623160

Error: 
Traceback (most recent call last):
Failure: twisted.internet.defer.TimeoutError: <twisted.python.test.test_sendmsg.SendmsgTests testMethod=test_sendSubProcessFD> (test_sendSubProcessFD) still running at 120.0 secs

twisted.python.test.test_sendmsg.SendmsgTests.test_sendSubProcessFD
===============================================================================
Error: 
Traceback (most recent call last):
Failure: twisted.trial.util.DirtyReactorAggregateError: Reactor was unclean.
Selectables:
<twisted.internet.process.ProcessWriter object at 0x0000000009197830>
<twisted.internet.process.ProcessReader object at 0x0000000009197868>
<twisted.internet.process.ProcessReader object at 0x00000000091978a0>

twisted.python.test.test_sendmsg.SendmsgTests.test_sendSubProcessFD
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[adiroiban]

I was not able to reproduce this error using cpython 3.12 $ trial -u -j8 twisted.python.test.test_sendmsg

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Yeah I can't reproduce it locally either. It was on pypy3.10-v7.3.14-no-coverage so possibly that is relevant; I haven't tried on PyPy.