Update CHANGELOG.md for 12.5.5

[ci skip]

CHANGELOG.md

@@ -2,6 +2,18 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
 
+## 12.5.5
+
+### Security (1 change)
+
+- Upgrade Akismet gem to v3.0.0. !21786
+
+### Fixed (2 changes)
+
+- Fix error in updating runner session. !20902
+- Fix Asana integration. !21501
+
+
 ## 12.5.4
 
 ### Security (1 change)

changelogs/unreleased/sh-fix-asana-integration.yml

----
-title: Fix Asana integration
-merge_request: 21501
-author:
-type: fixed

changelogs/unreleased/sh-fix-issue-34366.yml

----
-title: Fix error in updating runner session
-merge_request: 20902
-author:
-type: fixed

changelogs/unreleased/sh-upgrade-akismet-gem.yml

----
-title: Upgrade Akismet gem to v3.0.0
-merge_request: 21786
-author:
-type: security