Avoid bogus scans of partitions when validating FKs to partitioned tables

Avoid bogus scans of partitions when validating FKs to partitioned tables

Validating an unvalidated foreign key that references a partitioned
table would try to queue validations for each individual partition of
the referenced table, but this is wrong: each individual partition would
not necessarily have all the referenced rows, so errors would be raised.
Avoid doing that.  The pg_constraint rows that cause this to happen are
only there to support the action triggers that implement the DELETE/
UPDATE actions of the FK, so no validating scan is necessary.

This was an oversight in commit b663b9436e75.

An equivalent oversight exists for NOT ENFORCED constraints, which is
not fixed in this commit.

Author: Amul Sul <sulamul@gmail.com>
Reported-by: Antonin Houska <ah@cybertec.at>
Reviewed-by: jian he <jian.universality@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/26983.1748418675@localhost