pgsql: Fix EXCEPT publication test to check subscriber

Fix EXCEPT publication test to check subscriber

Commit fd366065e06 added tests intended to verify that rows inserted
on the publisher are replicated to the subscriber when using multiple
publications, with one excluding the target table via EXCEPT and
another including it.

However, the tests queried the publisher instead of the subscriber.
Since the rows were inserted directly into the publisher, the checks
would always succeed, providing no coverage of replication.

Fix this by querying the subscriber so the tests verify the replicated
state.

Author: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reviewed-by: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHGQGwGfXUO7f4t6KNGurYwg6QsnLtpP0K3EACbAwYWtxGfKfQ@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c5f1f41b52b60d4d27a9d77e074da553ee98e26e

Modified Files
--------------
src/test/subscription/t/037_except.pl | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)