pgsql: Improve objectNamesToOids() comment

Improve objectNamesToOids() comment

Commit d31bbfb6590 removed the comment at objectNamesToOids() that
there is no locking, because that commit added locking. But to fix
all the problems, we'd still need a stronger lock. So put the comment
back with more a detailed explanation.

Co-authored-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: /messages/by-id/bf72b82c-124d-4efa-a484-bb928e9494e4@eisentraut.org

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/118601a7e8c088306fe952ff298afd687483b35e

Modified Files
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src/backend/catalog/aclchk.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)