pgsql: Force COLLATE "C" to stabilize ordering in new test_pg_dump quer

Force COLLATE "C" to stabilize ordering in new test_pg_dump queries.

Should have thought of the need for this.

(Local testing suggests that we may still not be out of the
woods, but certainly this much is needed.)

Per buildfarm and David Rowley.

Discussion: https://postgr.es/m/CAApHDvo8pMk5WWFAqwGzuQ-Xh+957W61io_OsCP0oUzqCCODTg@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/900d1144256a63250a2e326567b636ee3220b731

Modified Files
--------------
src/test/modules/test_pg_dump/expected/test_pg_dump.out | 4 ++--
src/test/modules/test_pg_dump/sql/test_pg_dump.sql      | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)