Re: [PoC] pg_upgrade: allow to upgrade publisher node

FYI fairywren failed in this test:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=fairywren&dt=2023-12-16%2022%3A03%3A06

===8<===
Restoring database schemas in the new cluster
*failure*

Consult the last few lines of

"C:/tools/nmsys64/home/pgrunner/bf/root/HEAD/pgsql.build/testrun/pg_upgrade/003_logical_slots/data/t_003_logical_slots_newpub_data/pgdata/pg_upgrade_output.d/20231216T221418.035/log/pg_upgrade_dump_1.log"
for
the probable cause of the failure.
Failure, exiting
[22:14:34.598](22.801s) not ok 10 - run of pg_upgrade of old cluster
[22:14:34.600](0.001s) #   Failed test 'run of pg_upgrade of old cluster'
#   at C:/tools/nmsys64/home/pgrunner/bf/root/HEAD/pgsql/src/bin/pg_upgrade/t/003_logical_slots.pl
line 177.
===8<===

Without that log it might be hard to figure out what went wrong though :-/