Add changelog note

Author: github-actions[bot]

CHANGELOG.md

@@ -9,6 +9,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 ## 3.28.2 - 21 Jan 2025
 
 No user facing changes.
+- Update default CodeQL bundle version to 2.20.2. [#2707](https://github.com/github/codeql-action/pull/2707)
 
 ## 3.28.1 - 10 Jan 2025