Regression tests: nondeterministic ordering of relation names in DETAIL output causes spurious diffs

[eaydingol]

We have intermittent diffs caused only by the ordering of object names inside an error DETAIL line.
The underlying behavior/error is identical; only the printed order changes, which makes tests flaky across runs/platforms.

Example diff:

-DETAIL:  events_test_table_2 and users_test_table are not colocated
+DETAIL:  users_test_table and events_test_table_2 are not colocated

See examples from https://github.com/citusdata/citus/actions/runs/20709974469/job/59448186897?pr=8431

[onurctirtir]

5a71f0d was supposed to fix that already, strange that it's not the case ..