typo fix

Typo

(cherry picked from commit 4704077)

Author: johanrhodin

release-notes/3.13.4.md

@@ -104,7 +104,7 @@ Release notes can be found on GitHub at [rabbitmq-server/release-notes](https://
 
    GitHub issue: [#11524](https://github.com/rabbitmq/rabbitmq-server/pull/11524)
 
- * `rabbitmqctl list_unresponsive_queues` ran into exception of there were connected MQTT clients
+ * `rabbitmqctl list_unresponsive_queues` ran into an exception if there were connected MQTT clients
    with QoS 0 subscriptions.
 
    Partially contributed by @gomoripeti.