test_events: Run on_commit send_event hooks immediately.

Further commits will hook some `send_event` calls to `on_commit`.
With those changes, these will never be executed in tests, because
transactions never get commited with `TestCase`, which the
`ZulipTestCase` is a subclass of.

We want to make sure that these events are actually sent for testing
purposes, hence this change.

There's no need to actually capture the callbacks, because the
events are already thoroughly tested.

zerver/tests/test_events.py

@@ -276,7 +276,13 @@ def verify_action(
             include_subscribers=include_subscribers,
             include_streams=include_streams,
         )
-        action()
+
+        # We want even those `send_event` calls which have been hooked to
+        # `transaction.on_commit` to execute in tests.
+        # See the comment in `ZulipTestCase.tornado_redirected_to_list`.
+        with self.captureOnCommitCallbacks(execute=True):
+            action()
+
         events = client.event_queue.contents()
         content = {
             "queue_id": "123.12",