Why a `[native_extensions]` field in the `test/project/project.godot` ?

### Godot version

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### godot-cpp version

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### System information

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### Issue description

The `project.godot` in the tests contains a `[native_extensions]` entry:

https://github.com/godotengine/godot-cpp/blob/5910c0e8a2a1ab236016ccfb6983bf018470c4f3/test/project/project.godot#L18-L20

However, as far as I know, this entry has no use:
- searching for `native_extensions` in Godot and Godot-CPP source code doesn't return anything
- no other projects that I know of use this entry
- obviously not providing this entry doesn't prevent the extension from being loaded and used by Godot ;-)

So I think this entry should be removed, as it is misleading (especially since it is totally undocumented and Godot-CPP is most likely regarded as providing "the right way"® of doing thing regarding GDExtension usage)

### Steps to reproduce

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### Minimal reproduction project

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