Display 'Unknown' when runner.version is empty (#24378)
Before:
![image](https://user-images.githubusercontent.com/18380374/234782197-43d8f86d-afe2-4626-8e46-b621d7cde8f9.png)
After:
![image](https://user-images.githubusercontent.com/18380374/234782064-6828ae3b-5957-451f-82bb-22ab60b6c2a8.png)