Update changelog for v4.31.1

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]
+## 4.31.1 - 30 Oct 2025
 
 - The `add-snippets` input has been removed from the `analyze` action. This input has been deprecated since CodeQL Action 3.26.4 in August 2024 when this removal was announced.