### Godot version

Master (4.2)

### System information

Windows 11 - Vulkan - Nvidia RTX 4070 - intel i5 13600KF

### Issue description

As you can see in the video when you try to add multiple scenes in to the 3D viewport (only with multiple scenes) the editor throws this error.

```
ERROR: Can't add child '@Node3D@18837' to '@SubViewport@9274', already has a parent '@SubViewport@9274'.
   at: (scene\main\node.cpp:1411)
```


Video: https://youtu.be/BVcCIigQJDw

This happens in the latest master (pulled on 2.11.2023).

### Steps to reproduce

Drag couple of the 3d mesh scenes into the 3D viewport and then select multiple scenes and drag them over and observer the error.

### Minimal reproduction project

[TestSceneDragAndDrop.zip](https://github.com/godotengine/godot/files/13253741/TestSceneDragAndDrop.zip)

}
	/
	return world_pos + world_ray * FALLBACK_DISTANCE;
}
AABB Node3DEditorViewport::_calculate_spatial_bounds(const Node3D *p_parent, bool p_exclude_top_level_transform) {
	AABB bounds;
	const VisualInstance3D *visual_instance = Object::cast_to<VisualInstance3D>(p_parent);
	if (visual_instance) {
		bounds = visual_instance->get_aabb();
	}
	for (int i = 0; i < p_parent->get_child_count(); i++) {
		Node3D *child = Object::cast_to<Node3D>(p_parent->get_child(i));
		if (child) {
			AABB child_bounds = _calculate_spatial_bounds(child, false);
			if (bounds.size == Vector3() && p_parent) {
				bounds = child_bounds;
			} else {
				bounds.merge_with(child_bounds);
			}
		}
	}
	if (bounds.size == Vector3() && !p_parent) {
		bounds = AABB(Vector3(-0.2, -0.2, -0.2), Vector3(0.4, 0.4, 0.4));
	}
	if (!p_exclude_top_level_transform) {
		bounds = p_parent->get_transform().xform(bounds);
	}
	return bounds;
}
Node *Node3DEditorViewport::_sanitize_preview_node(Node *p_node) const {