### 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)

real_t tolerance = 0.001;
	bool equal = true;
	if (!Math::is_equal_approx(old_camera_cursor.x_rot, camera_cursor.x_rot, tolerance) || !Math::is_equal_approx(old_camera_cursor.y_rot, camera_cursor.y_rot, tolerance)) {
		equal = false;
	} else if (!old_camera_cursor.pos.is_equal_approx(camera_cursor.pos)) {
		equal = false;
	} else if (!Math::is_equal_approx(old_camera_cursor.distance, camera_cursor.distance, tolerance)) {
		equal = false;
	} else if (!Math::is_equal_approx(old_camera_cursor.fov_scale, camera_cursor.fov_scale, tolerance)) {
		equal = false;
	}
	if (!equal || p_interp_delta == 0 || is_orthogonal != orthogonal) {
		camera->set_global_transform(to_camera_transform(camera_cursor));
		if (orthogonal) {
			float half_fov = Math::deg_to_rad(get_fov()) / 2.0;
			float height = 2.0 * cursor.distance * Math::tan(half_fov);
			camera->set_orthogonal(height, get_znear(), get_zfar());
		} else {
			camera->set_perspective(get_fov(), get_znear(), get_zfar());
		}
		update_transform_gizmo_view();
		rotation_control->queue_redraw();
		position_control->queue_redraw();
		look_control->queue_redraw();
		spatial_editor->update_grid();
	}
}
Transform3D Node3DEditorViewport::to_camera_transform(const Cursor &p_cursor) const {