### Godot version

0810ecaafdbee3ea747219e6ab3a8de5d2216a09

### System information

Windows 11, Nvidia 3000, firefox

### Issue description

Exporting the gltf file is corrupt in blender.

### Steps to reproduce

1. Open project.
2. Export as glb
3. Open in blender
4. Blender display many warnings

![image](https://user-images.githubusercontent.com/32321/216740742-de662c5c-f5c3-44b5-a36e-8ad33defdbba.png)


### Minimal reproduction project

https://cdn.discordapp.com/attachments/598003845657788438/1071249610896580691/Test_Game_Project.zip


for (int i = 0; i < p_state->skins.size(); ++i) {
		for (int j = i + 1; j < p_state->skins.size(); ++j) {
			const Ref<Skin> skin_i = p_state->skins[i]->godot_skin;
			const Ref<Skin> skin_j = p_state->skins[j]->godot_skin;
			if (_skins_are_same(skin_i, skin_j)) {
				
				p_state->skins.write[j]->godot_skin = skin_i;
			}
		}
	}
}
Error GLTFDocument::_serialize_lights(Ref<GLTFState> p_state) {