Tiny fix for `check_self_hosted_runner.py` (#24052)

fix
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

utils/check_self_hosted_runner.py

@@ -25,7 +25,7 @@ def get_runner_status(target_runners, token):
         fp.write(json.dumps(offline_runners))
 
     if len(offline_runners) > 0:
-        failed = "\n".join(offline_runners)
+        failed = "\n".join([x["name"] for x in offline_runners])
         raise ValueError(f"The following runners are offline:\n{failed}")