[Bugfix] Update ComfyUI serving-mode mock after helper rename (#7694)

Signed-off-by: Linze-Shi <linzeshi0@gmail.com>

tests/e2e/features/comfyui/test_comfyui_integration.py

@@ -534,7 +534,7 @@ def mock_async_omni(
     # 1. The API layer uses its stage_list and stage_configs attributes
     # 2. Its __init__ method has slow side effects (model & config loading).
     # These cases use the non-duplex mock engine without loading model configs.
-    mocker.patch("vllm_omni.entrypoints.openai.api_server._is_duplex_model", return_value=False)
+    mocker.patch("vllm_omni.entrypoints.openai.api_server._should_serve_duplex", return_value=False)
     mock_async_omni_cls = mocker.patch("vllm_omni.entrypoints.openai.api_server.AsyncOmni")
     monkeypatch.setattr(
         "vllm_omni.entrypoints.openai.serving_chat.OmniOpenAIServingChat._preprocess_chat",