Add changelog note

Author: henrymercer

CHANGELOG.md

@@ -6,7 +6,7 @@ Note that the only difference between `v2` and `v3` of the CodeQL Action is the
 
 ## [UNRELEASED]
 
-No user facing changes.
+- Fixed an issue where setting up the CodeQL tools would sometimes fail with the message "Invalid value 'undefined' for header 'authorization'". [#2590](https://github.com/github/codeql-action/pull/2590)
 
 ## 3.27.1 - 08 Nov 2024