[9.16] Resolve "ThreadSanitizer: data race lib/dns/rbtdb.c:1365 in newversion"
Backport of !7637 (merged).
FTR: There are commits in !7637 (merged), which make sense for main
(and for v9_18
too), because they now process catalog zone updates with catzs->lock
unlocked, and they use "offload" threads for the update.
Those commits were not backported, because they are not useful in 9_16
.
Closes #3907 (closed)
Edited by Arаm Sаrgsyаn