pgsql: Validate ALTER PUBLICATION after acquiring the publication lock.

Validate ALTER PUBLICATION after acquiring the publication lock.

AlterPublicationOptions() can use stale publication state when the
publication is modified concurrently while waiting for the publication
lock. In particular, a concurrent ALTER PUBLICATION ... SET ALL TABLES
can change puballtables, causing the validation to make decisions based
on the old value and leads to assertion failure. Likewise,
CheckAlterPublication() could miss a table added concurrently, letting
SET ALL TABLES EXCEPT (...) leave pg_publication_rel with a mixture of
inclusion and exclusion rows.

Fix by acquiring the lock and re-reading the publication tuple in
AlterPublication() before either path runs, and by calling
CheckAlterPublication() only after that.

Also fix 037_except.pl, which left one computed result untested and
silently reused a subscription created by an earlier test.

Author: Vignesh C <vignesh21(at)gmail(dot)com>
Reviewed-by: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: shveta malik <shveta(dot)malik(at)gmail(dot)com>
Reviewed-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Discussion: https://postgr.es/m/CALDaNm1r2MkGu6h8zgU1Kj1sX-FcMQ7wGTeLSnhx-5joiyXEvg@mail.gmail.com
Backpatch-through: 19, where it was introduced

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5624de9904ca560c0d4473cb9e86108f4b69be38

Modified Files
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src/backend/commands/publicationcmds.c | 73 ++++++++++++++++++----------------
src/test/subscription/t/037_except.pl | 21 +++++-----
2 files changed, 51 insertions(+), 43 deletions(-)