message: [gha][lbt] change error when report empty
  Closes:
diff: @@ -212,7 +212,7 @@ jobs:
  console.error("Failed to check infra error in CT output log.\n", err);
  }
  } else {
  - body = "Cluster Test failed - test report processing failed.";
  + body = "Cluster Test runner failed.";
  console.error(err);
  }
  body += " See https://github.com/libra/libra/actions/runs/${{github.run_id}}";
  