Use personal access token for pushing

action bot not allowed to update github pages, see
https://github.community/t5/GitHub-Actions/Github-action-not-triggering-gh-pages-upon-push/td-p/26869

Author: dontcallmedom

.github/workflows/validate.yml

@@ -31,5 +31,5 @@ jobs:
     - name: Push changes
       if: github.ref == 'refs/heads/master'
       run: |
-        git remote set-url --push origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY
+        git remote set-url --push origin https://x-access-token:${{ secrets.W3C_GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY
         git push origin HEAD:master