fix e2e workflow to run on release branches

Author: itsankit-google

.github/workflows/e2e.yml

@@ -65,6 +65,7 @@ jobs:
         with:
           repository: cdapio/cdap-e2e-tests
           path: e2e
+          ref: release/6.11
 
       - name: Cache
         uses: actions/cache@v4