Mention Osiris upgrade to 1.2.4 in 3.9.13 release notes

Author: acogoluegnes

release-notes/3.9.13.md

@@ -24,8 +24,7 @@ TBD
 
 ## Dependency Upgrades
 
-TBD
-
+* Osiris was [upgraded to `1.2.4`](https://github.com/rabbitmq/osiris/compare/v1.2.3...v1.2.4)
 
 ## Source Code Archives