Update CHANGELOG entries for 8.11.5.

I've also removed some duplicates from 8.11.4.

CHANGELOG

@@ -104,13 +104,16 @@ v 8.12.0 (unreleased)
   - Use default clone protocol on "check out, review, and merge locally" help page URL
   - API for Ci Lint !5953 (Katarzyna Kobierska Urszula Budziszewska)
-v 8.11.5 (unreleased)
-  - Optimize branch lookups and force a repository reload for Repository#find_branch
-  - Fix member expiration date picker after update
-  - Make merge conflict file size limit 200 KB, to match the docs
+v 8.11.6 (unreleased)
+
+v 8.11.5
+  - Optimize branch lookups and force a repository reload for Repository#find_branch. !6087
+  - Fix member expiration date picker after update. !6184
   - Fix suggested colors options for new labels in the admin area. !6138
   - Fix GitLab import button
-  - Remove gitorious from import_sources
+  - Fix confidential issues being exposed as public using gitlab.com export
+  - Remove gitorious from import_sources. !6180
+  - Scope webhooks/services that will run for confidential issues
 v 8.11.4
   - Fix resolving conflicts on forks. !6082
@@ -124,10 +127,6 @@ v 8.11.4
   - Creating an issue through our API now emails label subscribers !5720
   - Block concurrent updates for Pipeline
   - Don't create groups for unallowed users when importing projects
-  - Fix resolving conflicts on forks
-  - Fix diff commenting on merge requests created prior to 8.10
-  - Don't create groups for unallowed users when importing projects
-  - Scope webhooks/services that will run for confidential issues
   - Fix issue boards leak private label names and descriptions
   - Fix broken gitlab:backup:restore because of bad permissions on repo storage !6098 (Dirk Hörner)
   - Remove gitorious. !5866