[Fix] Use utf-8 encoding in entrypoints/openai/run_batch.py (#5606)

Author: zifeitong

vllm/entrypoints/openai/run_batch.py

@@ -58,7 +58,7 @@ async def read_file(path_or_url: str) -> str:
                    session.get(path_or_url) as resp:
             return await resp.text()
     else:
-        with open(path_or_url, "r") as f:
+        with open(path_or_url, "r", encoding="utf-8") as f:
             return f.read()
 
 
@@ -71,7 +71,7 @@ async def write_file(path_or_url: str, data: str) -> None:
         # We should make this async, but as long as this is always run as a
         # standalone program, blocking the event loop won't effect performance
         # in this particular case.
-        with open(path_or_url, "w") as f:
+        with open(path_or_url, "w", encoding="utf-8") as f:
             f.write(data)