resolve pydantic error in startup benchmark (#31348)

Signed-off-by: Andy Xie <andy.xning@gmail.com>

tests/benchmarks/test_bench_startup.py

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import subprocess
+
+import pytest
+
+
+@pytest.mark.benchmark
+def test_bench_startup():
+    command = [
+        "vllm",
+        "bench",
+        "startup",
+    ]
+    result = subprocess.run(command, capture_output=True, text=True)
+    print(result.stdout)
+    print(result.stderr)
+
+    assert result.returncode == 0, f"Benchmark failed: {result.stderr}"