Context

Investigating ty's unused-awaitable rule (see
https://gist.github.com/blink1073/a9fe43fbb2643b12ab4472836e77ee40) found 2 real
missing-await bugs in test/asynchronous:
* ResetPoolThread.run() (test_client.py) never awaits self._run(), so the
pool-reset loop never executes during test_reset_during_update_pool.
* InsertEventListener.succeeded() (test_retryable_writes.py) never awaits
admin.command(...), so its configureFailPoint is never set.
Both tests pass without exercising the behavior they're meant to test.

mypy's unused-coroutine check should catch this but doesn't: mypy_test.ini
disables no-untyped-def for test.*, and mypy skips body-checking on
unannotated methods, which both of these are.

Definition of done

* Both bugs fixed; each test genuinely exercises its intended scenario
* Full test suite passes, including the two affected tests

Pitfalls

* ResetPoolThread.run() needs more than await: Thread.run() has no
running event loop, so it needs a real fix (e.g. dedicated loop in the thread, or
drop the raw Thread)
* Once the failpoint actually fires, test_retryable_writes.py may exercise a
new code path, confirm it still passes and still tests what it intends