ci: configure user name/email for GH Pages Cleanup

Author: cwillisf

.github/workflows/ghpages-cleanup.yml

@@ -26,6 +26,9 @@ jobs:
           done
           git status
       - name: Commit
-        run: "git commit -m 'chore: remove stale GitHub Pages branches'"
+        run: |
+          git config user.name 'github-actions[bot]'
+          git config user.email 'github-actions[bot]@users.noreply.github.com'
+          git commit -m 'chore: remove stale GitHub Pages branches'
       - name: Push
         run: "git push"