Resolver crashes caused by destroying locked mutexes

Since yesterday, all three RPZ-mode "stress" test jobs failed for main due to named crashing during the test:

• https://gitlab.isc.org/isc-projects/bind9/-/jobs/2953945
• https://gitlab.isc.org/isc-projects/bind9/-/jobs/2953948
• https://gitlab.isc.org/isc-projects/bind9/-/jobs/2953951

The error logged is:

01-Dec-2022 02:43:32.062 general: critical: adb.c:1188:destroy_adbentry(): fatal error: 
01-Dec-2022 02:43:32.062 general: critical: pthread_mutex_destroy(): Device or resource busy (16)
01-Dec-2022 02:43:32.062 general: critical: exiting (due to fatal error in library)

This most likely means that an dns_adbentry_t's lock mutex was still locked while its destruction was attempted.

These crashes did not happen for v9_18, so !7138 (merged) is the most likely culprit.

Job artifacts (including core dumps and binaries) were preserved.