ASYNC102 should allow aclose_forcefully

[A5rocks]

async def _run_handler(stream: StreamT, handler: Handler[StreamT]) -> None:
    try:
        await handler(stream)
    finally:
        await trio.aclose_forcefully(stream)  # E

this should be allowed, I think. It currently gets this error message:

src/trio/_highlevel_serve_listeners.py:36:9: ASYNC102 await inside try/finally on line 33 must have shielded cancel scope with a timeout.

but this relies on the implementation of aclose_forcefully, which is documented as cancelling immediately.

[A5rocks]

Same for trio.lowlevel.cancel_shielded_checkpoint, which the name suggests is shielded (and adding a timeout wouldn't make sense, since it's just a single tick).