Update 3.13.0 change log

(cherry picked from commit c046723b13d8e2c9b762e399aaea087aaee152ed)

Author: michaelklishin

release-notes/3.13.0.md

@@ -375,6 +375,7 @@ This release includes all bug fixes shipped in the `3.12.x` series.
 
  * `ra` was upgraded to [`2.7.1`](https://github.com/rabbitmq/ra/releases)
  * `osiris` was updated to [`1.7.2`](https://github.com/rabbitmq/osiris/releases)
+ * `cowboy` was updated to [`2.11.0`](https://ninenines.eu/docs/en/cowboy/2.11/guide/migrating_from_2.10/)
 
 ## Source Code Archives