Fix missing property decorator

Author: dangusev

plugins/gemini/vision_agents/plugins/gemini/gemini_realtime.py

@@ -112,6 +112,7 @@ def __init__(
         self._session: Optional[AsyncSession] = None
         self._receive_task: Optional[asyncio.Task[Any]] = None
 
+    @property
     def output_audio_track(self) -> AudioStreamTrack:
         return self._output_audio_track