style: format A2A route imports

Author: he-yufeng

src/google/adk/cli/fast_api.py

@@ -746,6 +746,7 @@ async def _get_a2a_runner_async() -> Runner:
       )
 
     import inspect
+
     from google.adk.agents import Agent
     import google.auth
     from pydantic import ValidationError as _ValidationError