Update CHANGELOG

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CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.3.0 (unreleased)
-  - Fix application settings cache not expiring after changes (Stan Hu)
   - Fix: Assignee selector is empty when 'Unassigned' is selected (Jose Corcuera)
   - Fix 500 error when update group member permission
   - Trim leading and trailing whitespace of milestone and issueable titles (Jose Corcuera)
@@ -12,6 +11,9 @@ v 8.3.0 (unreleased)
   - Expose events API with comment information and author info
   - Fix: Ensure "Remove Source Branch" button is not shown when branch is being deleted. #3583
 
+v 8.2.3
+  - Fix application settings cache not expiring after changes (Stan Hu)
+
 v 8.2.2
   - Fix 404 in redirection after removing a project (Stan Hu)
   - Ensure cached application settings are refreshed at startup (Stan Hu)