Fix SQL injection in logical replication origin checks.

Fix SQL injection in logical replication origin checks.

ALTER SUBSCRIPTION ... REFRESH PUBLICATION interpolates schema and
relation names into SQL without quoting them.  A crafted subscriber
relation name can inject arbitrary SQL on the publisher.  Test such a
name.  Back-patch to v16, where commit
875693019053b8897ec3983e292acbb439b088c3 first appeared.

Reported-by: Pavel Kohout <pavel.kohout@aisle.com>
Author: Pavel Kohout <pavel.kohout@aisle.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Backpatch-through: 16
Security: CVE-2026-6638