4.3.0 release notes update

[ci skip]

(cherry picked from commit 5753382)

Author: michaelklishin

release-notes/4.3.0.md

@@ -212,6 +212,11 @@ compared to other versions.
 
 #### Bug Fixes
 
+ * If a quorum queue with a large backlog terminated abnormally, node memory
+   footprint could spike.
+
+   GitHub issue: [#15837](https://github.com/rabbitmq/rabbitmq-server/pull/15837)
+
  * `rabbitmqctl forget_cluster_node` now removes all quorum queue and stream members (replicas)
    before proceeding to leave the metadata store cluster.