Does not work for me on Blender 3.6

I just installed the addon from your latest zip, copy pasted the `Repeat Grid` example into the Blender Text Editor and tried to run it. Unfortunately I got an error:
```
Error: Python: Traceback (most recent call last):
File "/Repeat Grid.py", line 5, in
File "/Users/robertosaccon/Library/Application Support/Blender/3.6/scripts/addons/geometry-script-main/api/tree.py", line 41, in build_tree
node_group.is_modifier = True
AttributeError: 'GeometryNodeTree' object has no attribute 'is_modifier'
```
did I do anything wrong ?

update: tried the other examples, same error.