Fix none-comparison (E711) warnings (#19745)

Signed-off-by: Xiaodong Ye <yeahdongcn@gmail.com>

python/sglang/eval/llama3_eval.py

@@ -86,7 +86,7 @@ class CustomAsyncHTTPXClient(httpx.AsyncClient):
 
 def get_client(provider):
     if provider not in "b10":
-        if os.getenv("OPENAI_API_KEY") == None:
+        if os.getenv("OPENAI_API_KEY") is None:
             os.environ["OPENAI_API_KEY"] = "EMPTY"
     return {
         "oai": AsyncOpenAI(base_url="http://127.0.0.1:8000/v1/"),