[9.20] fix: usr: Fix a possible issue with reponse policy zones and catalog zones

If a response policy zone (RPZ) or a catalog zone contained an
`$INCLUDE` directive, then manually reloading that zone could
fail to process the changes in the response policy or in the
catalog, respectively. This has been fixed.

Closes #5714

Backport of MR !11489

Merge branch 'backport-5714-zone_loaddone-rpz-and-catz-bugfix-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11496