Merge pull request #4420 from rabbitmq/mk-3.9.15-release-notes-update

Proactively add #4376 to release notes

release-notes/3.9.15.md

@@ -20,6 +20,16 @@ Contributors are encouraged to update them together with their changes. This hel
    GitHub issue: [#4371](https://github.com/rabbitmq/rabbitmq-server/pull/4371)
 
 
+### Prometheus Plugin
+
+#### Bug Fixes
+
+ * Prometheus collector could run into an exception early on node's
+   schema database sync.
+
+   GitHub issue: [#4376](https://github.com/rabbitmq/rabbitmq-server/pull/4376)
+
+
 ### Management Plugin
 
 #### Bug Fixes
@@ -33,7 +43,8 @@ Contributors are encouraged to update them together with their changes. This hel
 
 ## Dependency Upgrades
 
- * Ra was [upgraded to `2.0.6`](https://github.com/rabbitmq/ra/compare/v2.0.4...v2.0.6)
+ * `ra` upgraded [from `2.0.4` to `2.0.6`](https://github.com/rabbitmq/ra/compare/v2.0.4...v2.0.6)
+ * `prometheus` upgraded from [`4.8.1` to `4.8.2`](https://github.com/deadtrickster/prometheus.erl/compare/06425c21a39c1564164f1cc3fe5bdfa8b23b1f78...v4.8.2)
 
 
 ## Source Code Archives