[ci] Only sync Cling if run in root-project/root

Otherwise the secret is not available and we should not attempt to
sync anyway.

Author: hahnjo

.github/workflows/sync_cling.yml

@@ -11,6 +11,7 @@ on:
 
 jobs:
   sync-cling-history:
+    if: github.repository_owner == 'root-project'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout ROOT