gh-108724: Fix _PySemaphore_Wait call during thread deletion (#116483)

In general, when `_PyThreadState_GET()` is non-NULL then the current
thread is "attached", but there is a small window during
`PyThreadState_DeleteCurrent()` where that's not true:
tstate_delete_common() is called when the thread is detached, but before
current_fast_clear().

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>