postgresql{12,13}Packages.pg_safeupdate: 1.5 -> 1.4
pg_safeupdate was updated to 1.5 in #269755. v1.5 is not compatible with
PostgreSQL 12 and 13 anymore, so those were marked as broken.
However, this blocks anyone using PostgreSQL 12 or 13 with pg_safeupdate
from updating nixpkgs.
Instead, the old version should have been kept for PG 12 and 13.