Update CHANGELOG.md.

Author: mario-campos

CHANGELOG.md

@@ -4,7 +4,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 
 ## [UNRELEASED]
 
-- Updated the Action to log a warning if executing v3 but could be executing v4. This is to help users migrate to v4 of the CodeQL Action.
+- CodeQL Action v3 will be deprecated in December 2026.  The Action now logs a warning for customers who are running v3 but could be running v4. For more information, see [Upcoming deprecation of CodeQL Action v3](https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/).
 
 ## 4.31.2 - 30 Oct 2025