Update CHANGELOG.md for 13.9.5-ee

[ci skip]

CHANGELOG.md

@@ -551,6 +551,28 @@ entry.
 - Convert mattermost alert to pajamas. !56556
+## 13.9.5 (2021-03-31)
+
+### Security (6 changes)
+
+- Leave pool repository on fork unlinking.
+- Fixed XSS in merge requests sidebar.
+- Fix arbitrary read/write in AsciiDoctor and Kroki gems.
+- Prevent infinite loop when checking if collaboration is allowed.
+- Disable arbitrary URI and file reads in JSON validator.
+- Require POST request to trigger system hooks.
+
+### Removed (1 change)
+
+- Make HipChat project service do nothing. !57434
+
+### Other (3 changes)
+
+- Remove direct mimemagic dependency. !57387
+- Refactor MimeMagic calls to new MimeType class. !57421
+- Switch to using a fake mimemagic gem. !57443
+
+
 ## 13.9.4 (2021-03-17)
 ### Security (1 change)