### 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)

d["position_offset"] = position_offset;
			snap_data[sp] = d;
		}
	}
	PhysicsDirectSpaceState3D *ss = get_tree()->get_root()->get_world_3d()->get_direct_space_state();
	PhysicsDirectSpaceState3D::RayResult result;
	Array keys = snap_data.keys();
	/
	const float max_snap_height = 500.0;
	/
	bool snapped_to_floor = false;
	if (keys.size()) {
		/
		/
		for (int i = 0; i < keys.size(); i++) {
			Node *node = Object::cast_to<Node>(keys[i]);
			Node3D *sp = Object::cast_to<Node3D>(node);
			Dictionary d = snap_data[node];
			Vector3 from = d["from"];
			Vector3 to = from - Vector3(0.0, max_snap_height, 0.0);
			HashSet<RID> excluded = _get_physics_bodies_rid(sp);
			PhysicsDirectSpaceState3D::RayParameters ray_params;
			ray_params.from = from;
			ray_params.to = to;
			ray_params.exclude = excluded;
			if (ss->intersect_ray(ray_params, result)) {
				snapped_to_floor = true;
			}
		}
		if (snapped_to_floor) {