### 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)

case VIEW_TYPE_RIGHT: {
			if (orthogonal) {
				name = TTR("Right Orthogonal");
			} else {
				name = TTR("Right Perspective");
			}
		} break;
		case VIEW_TYPE_FRONT: {
			if (orthogonal) {
				name = TTR("Front Orthogonal");
			} else {
				name = TTR("Front Perspective");
			}
		} break;
		case VIEW_TYPE_REAR: {
			if (orthogonal) {
				name = TTR("Rear Orthogonal");
			} else {
				name = TTR("Rear Perspective");
			}
		} break;
	}
	if (auto_orthogonal) {
		
		name += TTR(" [auto]");
	}
	view_menu->set_text(name);
	view_menu->reset_size();
}
void Node3DEditorViewport::_compute_edit(const Point2 &p_point) {