Cannot use Unity 6+

When a version of Unity 6 or higher is installed (i.e. with a version number 6000.x.x), Cake.Unity prints the following warning and will not allow those versions of Unity to be used:

```
Unity Editor file version 6000.0.2.27625 is incorrect.
Expected first two numbers to be positive and third one to be non negative.
Path: C:/Program Files/Unity/Hub/Editor/6000.0.2f1/Editor/Unity.exe
```

