Use expecteddir option in _run_pg_regress() (#7582)

Fix check-arbitrary-configs tests failure with current REL_16_STABLE.
This is the same problem as described in #7573. I missed pg_regress call
in _run_pg_regress() in that PR.

Co-authored-by: Karina Litskevich <litskevichkarina@gmail.com>

src/test/regress/citus_tests/common.py

@@ -294,6 +294,9 @@ def _run_pg_regress(
         output_dir,
         "--use-existing",
     ]
+    if PG_MAJOR_VERSION >= 16:
+        command.append("--expecteddir")
+        command.append(output_dir)
     if extra_tests != "":
         command.append(extra_tests)