Another candidate:

commit a076e4f5e42b85664693191d04cfb33e2f9acfa5 (refs/bisect/bad) 
Author: Andrew Svetlov <andrew.svetlov@gmail.com>
Date:   Thu May 9 15:14:58 2019 -0400

    bpo-36802: Drop awrite()/aclose(), support await write() and await close() instead (#13099)

Before this commit, the test pass. After this commit, the test still pass but logs a warning:

vstinner@WIN C:\vstinner\python\master>python -m test test_asyncio -m test_drain_raises -v
(...)
test_drain_raises (test.test_asyncio.test_streams.StreamTests) ... Task exception was never retrieved
future: <Task finished name='Task-2' coro=<StreamWriter.drain() done, defined at C:\vstinner\python\master\lib\asyncio\streams.py:417> exception=ConnectionAbor
tedError(10053, 'An established connection was aborted by the software in your host machine', None, 10053, None)>
Traceback (most recent call last):
  File "C:\vstinner\python\master\lib\asyncio\streams.py", line 434, in drain
    await fut
  File "C:\vstinner\python\master\lib\asyncio\proactor_events.py", line 370, in _loop_writing
    self._write_fut = self._loop._proactor.send(self._sock, data)
  File "C:\vstinner\python\master\lib\asyncio\windows_events.py", line 488, in send
    ov.WSASend(conn.fileno(), buf, flags)
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine
ok
(...)
Tests result: SUCCESS