tests: fix async/test_connect.py deadlock in Python 3.12

There was a breaking change in `wait_closed()` in Python 3.12 that
caused some tests from test_connect to hang indefinitely. The reason for
that was the fact that `wait_closed()` was waiting for all handlers to
finish their execution, while the handler expected `stop_event` to be
set. `stop_event` was set only *after* `wait_closed()` would have
finished and returned the control, which caused a deadlock.

This commit fixes the deadlock by setting `stop_event` right before
calling for `conn.disconnect()`. This makes sense, because at that
moment handling more new requests is not needed as connection is going
to be closed.
The old call for `stop_event.set()` is kept for the unlikely case when
there was a connection error and the execution did not reach
`stop_event.set()` call in `try` block. If it was reached, this call
will be a noop.

[1]: python/cpython#104344

Signed-off-by: Mikhail Koviazin <[email protected]>

tests/test_asyncio/test_connect.py

@@ -166,12 +166,13 @@ async def _handler(reader, writer):
         await aserver.start_serving()
         try:
             await conn.connect()
+            stop_event.set()
             await conn.disconnect()
         except ConnectionError:
             finished.set()
             raise
         finally:
-            stop_event.set()
+            stop_event.set()  # Set stop_event in case of a connection error
             aserver.close()
             await aserver.wait_closed()
             await finished.wait()