Add issue for automated changelogs (google-gemini#21912)

Author: g-samroberts

.github/workflows/release-notes.yml

@@ -95,6 +95,8 @@ jobs:
             This PR contains the auto-generated changelog for the ${{ steps.release_info.outputs.VERSION }} release.
 
             Please review and merge.
+
+            Related to #18505
           branch: 'changelog-${{ steps.release_info.outputs.VERSION }}'
           base: 'main'
           team-reviewers: 'gemini-cli-docs, gemini-cli-maintainers'