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@paquier.xyz>
Discussion: https://postgr.es/m/20221003234111.4ob7yph6r4g4ywhu@awork3.anarazel.de
Backpatch-through: 12

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e750e413325e7e2d1979efd82c212e3a91025435
Author: Andres Freund <andres@anarazel.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(-)