[BugFix] Fix Python 3.9 Support (#23306)

Signed-off-by: Jared O'Connell <46976761+jaredoconnell@users.noreply.github.com>
Signed-off-by: Cyrus Leung <cyrus.tl.leung@gmail.com>
Co-authored-by: Cyrus Leung <cyrus.tl.leung@gmail.com>

vllm/benchmarks/lib/endpoint_request_func.py

@@ -9,7 +9,7 @@ import sys
 import time
 import traceback
 from dataclasses import dataclass, field
-from typing import Optional
+from typing import Optional, Union
 
 import aiohttp
 from tqdm.asyncio import tqdm
@@ -28,7 +28,7 @@ class RequestFuncInput:
     model_name: Optional[str] = None
     logprobs: Optional[int] = None
     extra_body: Optional[dict] = None
-    multi_modal_content: Optional[dict | list[dict]] = None
+    multi_modal_content: Optional[Union[dict, list[dict]]] = None
     ignore_eos: bool = False
     language: Optional[str] = None
     request_id: Optional[str] = None