Another (minor) 4.2.0 release notes fix

Author: michaelklishin

release-notes/4.2.0.md

@@ -337,7 +337,7 @@ compared to other versions.
 
 #### Enhancements
 
- * `rabbitmq-diagnostics ` is a new command that provides a message size distribution.
+ * `rabbitmq-diagnostics message_size_stats` is a new command that provides a message size distribution.
    Use it to get an estimate of the size of the messages flowing through the cluster.
 
    GitHub issue: [#14560](https://github.com/rabbitmq/rabbitmq-server/pull/14560)