Update changelog for 16.8.6

[ci skip]

Author: GitLab Release Tools Bot

CHANGELOG.md

@@ -131,6 +131,10 @@ No changes.
 - [Update PostgreSQL 13 and 14](gitlab-org/omnibus-gitlab@8d6a65a402e0aa6fc7f826c424cb778f3e0d8b79)
 - [Update libxml2 from 2.10.4 to 2.12.3](gitlab-org/omnibus-gitlab@18f0dcced0f8597992b87bb0b01ae5d9f782842f)
 
+## 16.8.6 (2024-04-09)
+
+No changes.
+
 ## 16.8.5 (2024-03-27)
 
 ### Security (1 change)