Update example group: value to match GitHub's recommendation

Author: tianon

scripts/github-actions/example-ci.yml

@@ -12,7 +12,7 @@ defaults:
     shell: 'bash -Eeuo pipefail -x {0}'
 
 concurrency:
-  group: ${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 permissions: