Add gen_batch_server version bump to 3.10.x release notes

Author: HoloRin

release-notes/3.10.0.md

@@ -229,3 +229,4 @@ This release includes all bug fixes that shipped in `3.9.x` releases.
  * `osiris` upgraded from [`1.0.0` to `1.2.4`](https://github.com/rabbitmq/osiris/compare/v1.0.0...v1.2.4)
  * `ranch` upgraded from [`2.0.0` to `2.1.0`](https://github.com/ninenines/ranch/compare/2.0.0...2.1.0)
  * `observer_cli` upgraded from [`1.6.2` to `1.7.2`](https://github.com/zhongwencool/observer_cli/compare/1.6.2...1.7.2)
+ * `gen_batch_server` upgraded from [`0.8.6` to `0.8.7`](https://github.com/rabbitmq/gen-batch-server/compare/38191672ee0f22a8d5291c6c09f8c07178d565ca...v0.8.7)