pgsql: Fix regression test failure when wal_level is set to minimal.

Fix regression test failure when wal_level is set to minimal.

Commit 67c209 removed the WARNING for insufficient wal_level from the
expected output, but the WARNING may still appear on buildfarm members
that run with wal_level=minimal.

To avoid unstable test output depending on wal_level, this commit the
test to use ALTER PUBLICATION for verifying the same behavior,
ensuring the output remains consistent regardless of the wal_level
setting.

Per buildfarm member thorntail.

Author: Zhijie Hou <houzj(dot)fnst(at)fujitsu(dot)com>
Discussion: https://postgr.es/m/TY4PR01MB16907680E27BAB146C8EB1A4294B2A@TY4PR01MB16907.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0de5f0d869d1e06f172f10adf441e504174cf2fe

Modified Files
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src/test/regress/expected/publication.out | 8 +++-----
src/test/regress/sql/publication.sql | 6 ++----
2 files changed, 5 insertions(+), 9 deletions(-)