Update changelog for v4.31.12

Author: github-actions[bot]

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 See the [releases page](https://github.com/github/codeql-action/releases) for the relevant changes to the CodeQL CLI and language packs.
 
-## [UNRELEASED]
+## 4.31.12 - 26 Jan 2026
 
 - Update default CodeQL bundle version to [2.24.0](https://github.com/github/codeql-action/releases/tag/codeql-bundle-v2.24.0). [#3425](https://github.com/github/codeql-action/pull/3425)