### 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)

Node3DEditorSelectedItem *se = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(sp);
		if (!se) {
			continue;
		}
		if (sp->has_meta("_edit_lock_")) {
			continue;
		}
		if (se->gizmo.is_valid()) {
			for (KeyValue<int, Transform3D> &GE : se->subgizmos) {
				Transform3D xform = GE.value;
				Transform3D new_xform = _compute_transform(_edit.mode, se->original * xform, xform, p_motion, p_snap, local_coords, _edit.plane != TRANSFORM_VIEW); /
				if (!local_coords) {
					new_xform = se->original.affine_inverse() * new_xform;
				}
				se->gizmo->set_subgizmo_transform(GE.key, new_xform);
			}
		} else {
			Transform3D new_xform = _compute_transform(_edit.mode, se->original, se->original_local, p_motion, p_snap, local_coords, sp->get_rotation_edit_mode() != Node3D::ROTATION_EDIT_MODE_BASIS && _edit.plane != TRANSFORM_VIEW);
			_transform_gizmo_apply(se->sp, new_xform, local_coords);
		}
	}
	spatial_editor->update_transform_gizmo();
	surface->queue_redraw();
}
/
void Node3DEditorViewport::update_transform(bool p_shift) {
	Vector3 ray_pos = _get_ray_pos(_edit.mouse_pos);
	Vector3 ray = _get_ray(_edit.mouse_pos);
	double snap = EDITOR_GET("interface/inspector/default_float_step");
	int snap_step_decimals = Math::range_step_decimals(snap);