fix provider model list test (#800)

Fixes provider tests

```
pytest -v -s -k "together or fireworks or ollama" --inference-model="meta-llama/Llama-3.1-8B-Instruct" ./llama_stack/providers/tests/inference/test_text_inference.py 
```
```
...
.... 
llama_stack/providers/tests/inference/test_text_inference.py::TestInference::test_chat_completion_streaming[-together] PASSED
llama_stack/providers/tests/inference/test_text_inference.py::TestInference::test_chat_completion_with_tool_calling[-together] PASSED
llama_stack/providers/tests/inference/test_text_inference.py::TestInference::test_chat_completion_with_tool_calling_streaming[-together] PASSED

================ 21 passed, 6 skipped, 81 deselected, 5 warnings in 32.11s =================
```

Co-authored-by: Hardik Shah <hjshah@fb.com>

llama_stack/providers/tests/inference/test_text_inference.py

@@ -31,7 +31,7 @@ from llama_stack.apis.inference import (
     ToolChoice,
     UserMessage,
 )
-from llama_stack.apis.models import Model
+from llama_stack.apis.models import ListModelsResponse, Model
 
 from .utils import group_chunks
 
@@ -92,12 +92,13 @@ class TestInference:
     async def test_model_list(self, inference_model, inference_stack):
         _, models_impl = inference_stack
         response = await models_impl.list_models()
-        assert isinstance(response, list)
-        assert len(response) >= 1
-        assert all(isinstance(model, Model) for model in response)
+        assert isinstance(response, ListModelsResponse)
+        assert isinstance(response.data, list)
+        assert len(response.data) >= 1
+        assert all(isinstance(model, Model) for model in response.data)
 
         model_def = None
-        for model in response:
+        for model in response.data:
             if model.identifier == inference_model:
                 model_def = model
                 break