Update CHANGELOG

CHANGELOG

@@ -57,6 +57,7 @@ v 8.10.0 (unreleased)
   - Throttle the update of `project.pushes_since_gc` to 1 minute.
   - Allow expanding and collapsing files in diff view (!4990)
   - Collapse large diffs by default (!4990)
+  - Fix mentioned users list on diff notes
   - Check for conflicts with existing Project's wiki path when creating a new project.
   - Show last push widget in upstream after push to fork
   - Cache todos pending/done dashboard query counts.