pg_upgrade: check for old polymorphics from pre-14

When Who What
2022-07-05 17:08:13 Tom Lane (tgl) Closed in commitfest 2022-07 with status: Committed
2022-07-01 22:21:47 Tom Lane (tgl) Added tgl as committer
2022-06-27 23:32:49 Justin Pryzby (justinpryzby) Changed reviewers to Andrey Borodin (x4m)
2022-06-27 23:32:49 Justin Pryzby (justinpryzby) Changed authors to Justin Pryzby (justinpryzby)
2022-06-27 23:32:49 Justin Pryzby (justinpryzby) Changed targetversion to 14
2022-06-27 23:32:09 Justin Pryzby (justinpryzby) Attached mail thread 3383880.QJadu78ljV@vejsadalnx
2022-06-27 23:32:08 Justin Pryzby (justinpryzby) Created patch record