pgsql: Don't attempt to upgrade bpchar indexes from versions before 14.

Don't attempt to upgrade bpchar indexes from versions before 14.

As of a32b8dc98 and friends, amcheck will complain about bpchar
indexes that claim to allow de-duplication. This causes our
cross-version-upgrade tests to fail when upgrading from a version
that lacks those commits, since there are some such indexes in the
core regression tests. Drop such indexes from the upgrade source
database. (oidvector indexes would be problematic too, but
there aren't any user-defined indexes on oidvector in our tests.)

Author: Peter Geoghegan <pg(at)bowt(dot)ie>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAH2-Wzk-oO3HjLaByo8Vpse6Tpha1mqAW8DFShh-kS-Wo59ugA@mail.gmail.com
Backpatch-through: 14

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/4f1751879d34b35f6d33b338148d9ae7a57104d6

Modified Files
--------------
src/test/perl/PostgreSQL/Test/AdjustUpgrade.pm | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)