[4.0] Project converter: Embedded ButtonGroup subresources in scene get clobbered

[nobuyukinyuu]

Godot version

4.0

System information

Windows 10

Issue description

Note: This may apply to other subresources which were embedded in a scene rather than saved separately. I can update this issue if many should be classified together.

ButtonGroup subresources embedded in a scene rather than saved separately appear to get clobbered when using the project converter.

Steps to reproduce

Migrate project from 3.x to 4.0

Minimal reproduction project

n/a