tests: setUp overrides should call super().setUp().

MigrationsTestCase is intentionally omitted from this, since migrations
tests are different in their nature and so whatever setUp()
ZulipTestCase may do in the future, MigrationsTestCase may not
necessarily want to replicate.

zerver/tests/test_external.py

@@ -48,6 +48,7 @@ class MITNameTest(ZulipTestCase):
 class RateLimitTests(ZulipTestCase):
 
     def setUp(self) -> None:
+        super().setUp()
         settings.RATE_LIMITING = True
         add_ratelimit_rule(1, 5)