Mention CQ shutdown increase in 3.8.23/3.9.6 notes

Author: Loïc Hoguin

release-notes/3.8.23.md

@@ -45,10 +45,16 @@ consistent release schedule.
 
 #### Bug Fixes
 
-* TLS information delivered in [Proxy protocol](https://www.rabbitmq.com/networking.html#proxy-protocol) header is now attached to connection metrics as if it was provided by a non-proxying client.
+ * TLS information delivered in [Proxy protocol](https://www.rabbitmq.com/networking.html#proxy-protocol) header is now attached to connection metrics as if it was provided by a non-proxying client.
 
    GitHub issue: [#3175](https://github.com/rabbitmq/rabbitmq-server/pull/3175) contributed by @prefiks, sponsored by CloudAMQP
 
+ * Classic queue shutdown now uses a much higher timeout (up to 10 minutes instead of 30 seconds).
+
+   In environments with many queues (especially mirrored queues) and many consumers this means that
+   the chance of queue indices rebuilding after node restart is now substantially lower.
+
+   GitHub issue: [#3409](https://github.com/rabbitmq/rabbitmq-server/pull/3409)
 
 
 ## Dependency Upgrades

release-notes/3.9.6.md

@@ -29,6 +29,13 @@ Contributors are encouraged to update them together with their changes. This hel
 
    GitHub issue: [#3340](https://github.com/rabbitmq/rabbitmq-server/pull/3340)
 
+ * Classic queue shutdown now uses a much higher timeout (up to 10 minutes instead of 30 seconds).
+
+   In environments with many queues (especially mirrored queues) and many consumers this means that
+   the chance of queue indices rebuilding after node restart is now substantially lower.
+
+   GitHub issue: [#3409](https://github.com/rabbitmq/rabbitmq-server/pull/3409)
+
 
 ## Dependency Upgrades