fix ollama integration by forcing flat messages (#406)

src/smolagents/models.py

@@ -690,6 +690,7 @@ class LiteLLMModel(Model):
             api_base=self.api_base,
             api_key=self.api_key,
             convert_images_to_image_urls=True,
+            flatten_messages_as_text=self.model_id.startswith("ollama"),
             custom_role_conversions=self.custom_role_conversions,
             **kwargs,
         )