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_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/b0e087cfe48f042a54490e23ae312de5c0715c3b

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