queue: Do test retries in tests.

The lambda passed to `queue_json_publish` is used if
`settings.USING_RABBITMQ` is unset -- which is only true in tests.  As
such, this pattern causes failures to never actually retry within
tests.

This behaviour has existed ever since the outgoing webhook code was
introduced in 53a8b2ac87, with no explanation.  Not passing that
argument allows tests to verify the retry behaviour when webhooks
fail.

zerver/lib/queue.py

@@ -437,4 +437,4 @@ def retry_event(
     if event["failed_tries"] > MAX_REQUEST_RETRIES:
         failure_processor(event)
     else:
-        queue_json_publish(queue_name, event, lambda x: None)
+        queue_json_publish(queue_name, event)