ruff found issues

src/trio/_channel.py:(179:12 - 179:23): Cannot determine type of "_closed" [has-type]

src/trio/_channel.py:(247:12 - 247:23): Cannot determine type of "_closed" [has-type]

src/trio/_channel.py:(275:12 - 275:23): Cannot determine type of "_closed" [has-type]

src/trio/_channel.py:482: Unused "type: ignore" comment [unused-ignore]

src/trio/_channel.py:493: Unused "type: ignore" comment [unused-ignore]

src/trio/_channel.py:509: Unused "type: ignore" comment [unused-ignore]

src/trio/_tests/test_highlevel_serve_listeners.py:(45:15 - 45:46): "Tuple[MemorySendChannel[StapledStream[MemorySendStream, MemoryReceiveStream]], MemoryReceiveChannel[StapledStream[MemorySendStream, MemoryReceiveStream]]]" has no attribute "send_channel" [attr-defined]

src/trio/_tests/test_highlevel_serve_listeners.py:(53:24 - 53:58): "Tuple[MemorySendChannel[StapledStream[MemorySendStream, MemoryReceiveStream]], MemoryReceiveChannel[StapledStream[MemorySendStream, MemoryReceiveStream]]]" has no attribute "receive_channel" [attr-defined]

src/trio/_tests/test_highlevel_serve_listeners.py:(55:9 - 55:21): Returning Any from function declared to return "StapledStream[MemorySendStream, MemoryReceiveStream]" [no-any-return]

The following actions uses Node.js version which is deprecated and will be forced to run on node20: codecov/codecov-action@v3. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/