AssertionError in Deferred.send() (assert self._debugInfo is not None)

[thevintik]

Describe the incorrect behavior you saw
Wrong error (AssertionError) raises when Deferred is awaited.

Describe how to cause this behavior

    async def test_error_observation_after_deferredlist(self):
        @contextlib.asynccontextmanager
        async def async_contextmanager():
            await threads.deferToThread(lambda: None)
            try:
                yield
            finally:
                await threads.deferToThread(lambda: None)

        async def coro():
            async with async_contextmanager():
                raise RuntimeError

        deferred = defer.Deferred.fromCoroutine(coro())

        with self.assertRaises(defer.FirstError):
            await defer.DeferredList([deferred], fireOnOneErrback=True, consumeErrors=False)

        with self.assertRaises(RuntimeError):
            await deferred

  File "/home/user/test.py", line 32, in test_error_observation_after_deferredlist
    await deferred
  File "/home/user/.venv/lib/python3.12/site-packages/twisted/internet/defer.py", line 1174, in send
    assert self._debugInfo is not None
builtins.AssertionError:

Complete test file is at https://gist.github.com/thevintik/00e8bef71635690f6a05be724b894c8d

Describe the correct behavior you'd like to see
Original error (RuntimeError) should be raised on await, not an AssertionError.

Testing environment

• OS-independent (reproduces on both Windows and Linux)
• Twisted version 23.10.0 (also reproduces on 22.10.0)