BUG #19338: [PG15] Unstable SQL result in test regress/tablespace

The following bug has been logged on the website:

Bug reference: 19338
Logged by: Dmitry Kovalenko
Email address: d(dot)kovalenko(at)postgrespro(dot)ru
PostgreSQL version: 15.15
Operating system: AltLinux-10 ARM64
Description:

Hello!

PG15 has an unstable SQL in test regress/tablespace:

^^^^^^^^^^^^^^^^^^^^/home/test/.../src/test/regress/regression.diffs
diff -U3 /home/test/.../src/test/regress/expected/tablespace.out
/home/test/.../src/test/regress/results/tablespace.out
--- /home/test/.../src/test/regress/expected/tablespace.out 2025-11-30
21:11:56.000000000 +0300
+++ /home/test/.../src/test/regress/results/tablespace.out 2025-11-30
23:17:49.378004420 +0300
@@ -334,9 +334,9 @@
where c.reltablespace = t.oid AND c.relname LIKE 'part%_idx';
relname | spcname
-------------+------------------
+ part_a_idx | regress_tblspace
part1_a_idx | regress_tblspace
part2_a_idx | regress_tblspace
- part_a_idx | regress_tblspace
(3 rows)

\d testschema.part
^^^^^^^^^^^^^^^^^^^^

https://github.com/postgres/postgres/blob/134a8ee2240557e8165cffe70d19e48937cece03/src/test/regress/sql/tablespace.sql#L228

---
PG16 has the correct SQL:
...
where c.reltablespace = t.oid AND c.relname LIKE 'part%_idx' ORDER BY
relname;

https://github.com/postgres/postgres/blob/4d288e33b957ce5023dd1ec24b53f02c8a9e8ba0/src/test/regress/sql/tablespace.sql#L226

Could you backport this fix from PG16 to PG15, please?

Thanks&Regards,
Dmitry Kovalenko