add missing return statement

Author: ohmayr

google/auth/aio/transport/aiohttp.py

@@ -46,7 +46,7 @@ def _remaining_time():
         remaining = total_timeout - elapsed
         if remaining <= 0:
             raise TimeoutError(f"Context manager exceeded the configured timeout of {total_timeout}s.")
-        remaining
+        return remaining
 
     async def with_timeout(coro):
         try: