Update 3.12.0 release notes

Author: michaelklishin

release-notes/3.12.0.md

@@ -106,7 +106,7 @@ in the `3.11.x` release series.
  * Reduced memory footprint, improved memory use predictability and throughput of classic queues.
    This particularly benefits classic queues with longer backlogs.
 
-   GitHub issue: [#4522](https://github.com/rabbitmq/rabbitmq-server/pull/4522)
+   GitHub issues: [#4522](https://github.com/rabbitmq/rabbitmq-server/pull/4522), [#7516](https://github.com/rabbitmq/rabbitmq-server/pull/7516)
 
  * Reduced peak memory footprint of quorum queues.