Fix CHANGELOG

Remove duplicate 8.11.4 entries and mark 8.11.3 as released.

[ci skip]

CHANGELOG

@@ -51,14 +51,10 @@ v 8.12.0 (unreleased)
 v 8.11.4 (unreleased)
   - Fix broken gitlab:backup:restore because of bad permissions on repo storage !6098 (Dirk Hörner)
   - Creating an issue through our API now emails label subscribers !5720
-
-v 8.11.4 (unreleased)
   - Fix resolving conflicts on forks
-
-v 8.11.4 (unreleased)
   - Fix diff commenting on merge requests created prior to 8.10
 
-v 8.11.3 (unreleased)
+v 8.11.3
   - Do not enforce using hash with hidden key in CI configuration. !6079
   - Allow system info page to handle case where info is unavailable
   - Label list shows all issues (opened or closed) with that label