fix: dev: Disassociate added rdataset on error in cache_rrset()

When first dns_db_addrdataset() succeeds in cache_rrset(), but the
second one fails with error, the added rdataset was kept associated.
This caused assertion failure down the pipe in fctx_sendevents().

Merge branch 'ondrej/disassociate-added-on-error-in-cache_rrset' into 'main'

See merge request isc-projects/bind9!10861