PYTHON-5090 Convert test.test_monitor to async

[sleepyStick]

[sleepyStick]

okay in summary, we need the unmanaged async client for the test, because we want to test that the executors get GCd on client del and client.close. if we used managed, the client will not get GCd. on pypy GC is non-deterministic hence the failure. with that said, i believe the only failure is because of that and we should either skip this test in pypy (if so how?) or do something else to mitigate the failing test?

[sleepyStick]

The windows test failures are from test_connection_monitoring and test_async_cancellation, neither of which relate to this PR to my knowledge :)