Update 3.9.0 release notes for rc.2

Author: HoloRin

site/release-notes/3.9.0.md

@@ -1,6 +1,6 @@
-# RabbitMQ 3.9.0-rc.1
+# RabbitMQ 3.9.0-rc.2
 
-RabbitMQ `3.9.0-rc.1` is a candidate of a minor (feature) release. It contains new features,
+RabbitMQ `3.9.0-rc.2` is a candidate of a minor (feature) release. It contains new features,
 [support for Erlang 24](https://blog.rabbitmq.com/posts/2021/03/erlang-24-support-roadmap/),
 improved integration with our [RabbitMQ Kubernetes Operator](https://blog.rabbitmq.com/posts/2020/11/rabbitmq-kubernetes-operator-reaches-1-0/),
 and important internal changes in a number of subsystems.
@@ -211,6 +211,10 @@ Any questions about this release, upgrades or RabbitMQ in general are welcome on
 
    GitHub issue: [#3099](https://github.com/rabbitmq/rabbitmq-server/pull/3099)
 
+ * Correct an issue where the `num_acceptors.ssl` configuration value was applied
+   incorrectly
+
+   GitHub issue: [#3180](https://github.com/rabbitmq/rabbitmq-server/pull/3180)
 
 ### Kubernetes