fix: usr: Fix race condition when canceling ADB find

When canceling the ADB find, the lock on the find gets released for
a brief period of time to be locked again inside adbname lock.  During
the brief period that the ADB find is unlocked, it can get canceled by
other means removing it from the adbname list which in turn causes
assertion failure due to a double removal from the adbname list.
This has been fixed.

Closes #5024

Merge branch '5024-fix-crash-in-dns_adb_cancelfind' into 'main'

See merge request isc-projects/bind9!9722