Add CHANGELOG item for labels/milestones navigation change

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

CHANGELOG

@@ -63,6 +63,7 @@ v 8.9.0 (unreleased)
   - Toggling a task list item in a issue/mr description does not creates a Todo for mentions
   - Improved UX of date pickers on issue & milestone forms
   - Cache on the database if a project has an active external issue tracker.
+  - Put project Labels and Milestones pages links under Issues and Merge Requests tabs as subnav
 
 v 8.8.5 (unreleased)
   - Ensure branch cleanup regardless of whether the GitHub import process succeeds