test: 在模拟赛马测试中添加假机器人实例

为模拟赛马命令的测试环境添加一个 `_FakeBot` 实例，以更真实地模拟机器人交互场景。

danding_bot/plugins/group_horse_racing/test_commands.py

@@ -224,6 +224,7 @@ async def handle_test_simulate_race(bot: Bot, event: Event):
     fake_room_store = _InMemoryRoomStore()
     fake_points_service = _InMemoryPointsService()
     fake_message_service = _NoopMessageService()
+    fake_bot = _FakeBot()
 
     start_task: asyncio.Task | None = None
     room = None