[CI] Fix MHA attention test failure (AttributeError when model_config is None...

[CI] Fix MHA attention test failure (AttributeError when model_config is None in ViT attention backend) (#33033)
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>

vllm/model_executor/models/vision.py

@@ -104,8 +104,9 @@ def get_vit_attn_backend(
     """
     try:
         vllm_config: VllmConfig = get_current_vllm_config()
+        model_config = vllm_config.model_config
         multimodal_config: MultiModalConfig | None = (
-            vllm_config.model_config.multimodal_config
+            model_config.multimodal_config if model_config is not None else None
         )
     except AssertionError:
         multimodal_config = None
@@ -129,8 +130,9 @@ def is_vit_use_data_parallel():
     """
     try:
         vllm_config: VllmConfig = get_current_vllm_config()
+        model_config = vllm_config.model_config
         multimodal_config: MultiModalConfig | None = (
-            vllm_config.model_config.multimodal_config
+            model_config.multimodal_config if model_config is not None else None
         )
     except AssertionError:
         multimodal_config = None