fix async test

Author: phact

client/tests/astra-assistants/test_streaming_run_retrieval_async_v2.py

@@ -86,7 +86,7 @@ async def on_run_step_done(self, run_step) -> None:
             for tool_call in run_step.step_details.tool_calls:
                 matches = tool_call.file_search
                 print(tool_call.file_search)
-            assert len(matches) > 0, "No matches found"
+            assert len(matches.chunks) > 0, "No matches found"
 
         @override
         async def on_text_created(self, text) -> None: