Add changelog note

Author: github-actions[bot]

CHANGELOG.md

@@ -6,7 +6,7 @@ Note that the only difference between `v2` and `v3` of the CodeQL Action is the
 
 ## [UNRELEASED]
 
-No user facing changes.
+- Update default CodeQL bundle version to 2.16.5. [#2203](https://github.com/github/codeql-action/pull/2203)
 
 ## 3.24.8 - 18 Mar 2024