Add fork check to copilot-maintenance workflow (#24082)

Author: Copilot

.github/workflows/copilot-maintenance.yml

@@ -24,6 +24,7 @@ jobs:
   delete-old-copilot-branches:
     name: Delete Old Copilot Branches
     runs-on: ubuntu-latest
+    if: github.repository == 'github/gh-aw'
     steps:
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2