pgsql: tests: Restrict pg_locks queries in advisory_locks.sql to curren

tests: Restrict pg_locks queries in advisory_locks.sql to current database

Otherwise testing an existing installation can fail, if there are other locks,
e.g. from one of the isolation tests.

This was originally applied as c3315a7da57b in 16~, but it is possible
to see this test fail depending on the concurrent activity for older
active branches.

Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/20221003234111.4ob7yph6r4g4ywhu@awork3.anarazel.de
Backpatch-through: 12

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/3981fd5869fc78296133bba5fd28586684835e5c
Author: Andres Freund <andres(at)anarazel(dot)de>

Modified Files
--------------
src/test/regress/expected/advisory_lock.out | 31 ++++++++++++++--------------
src/test/regress/sql/advisory_lock.sql | 32 +++++++++++++++--------------
2 files changed, 33 insertions(+), 30 deletions(-)