Error with MakePrimitiveEditable.cs with Unity 2019.3.5

Hello,

There is an error in the example when running Unity 2019.3.5

```
Assets\Samples\ProBuilder\4.3.0-preview.4\Runtime Examples\Convert Mesh to Editable\MakePrimitiveEditable.cs(24,20): error CS1503: Argument 1: cannot convert from 'UnityEngine.Mesh' to 'UnityEngine.GameObject'
```