Add changelog note

Author: github-actions[bot]

CHANGELOG.md

@@ -5,6 +5,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 ## [UNRELEASED]
 
 - Update the action to prefer `gtar` over `tar` to make zstd archive extraction more robust. [2767](https://github.com/github/codeql-action/pull/2767)
+- Update default CodeQL bundle version to 2.20.5. [#2772](https://github.com/github/codeql-action/pull/2772)
 
 ## 3.28.9 - 07 Feb 2025