docker-compose example: use node:20-bookworm instead of the default

.forgejo/workflows/example-docker-compose.yml

@@ -60,6 +60,8 @@ jobs:
             sleep 30
           done
           grep --quiet "$success" /tmp/out
+          $cli logs runner-daemon > /tmp/runner.log
+          grep --quiet 'Start image=node:20-bookworm' /tmp/runner.log
 
       - name: full docker compose logs
         if: always()