### 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)

viewport = p_viewport;
}
void ViewportRotationControl::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_ENTER_TREE: {
			axis_menu_options.clear();
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_RIGHT);
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_TOP);
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_FRONT);
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_LEFT);
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_BOTTOM);
			axis_menu_options.push_back(Node3DEditorViewport::VIEW_REAR);
			axis_colors.clear();
			axis_colors.push_back(get_theme_color(SNAME("axis_x_color"), EditorStringName(Editor)));
			axis_colors.push_back(get_theme_color(SNAME("axis_y_color"), EditorStringName(Editor)));
			axis_colors.push_back(get_theme_color(SNAME("axis_z_color"), EditorStringName(Editor)));
			queue_redraw();
			if (!is_connected("mouse_exited", callable_mp(this, &ViewportRotationControl::_on_mouse_exited))) {
				connect("mouse_exited", callable_mp(this, &ViewportRotationControl::_on_mouse_exited));
			}
		} break;
		case NOTIFICATION_DRAW: {
			if (viewport != nullptr) {
				_draw();
			}
		} break;
	}
}
void ViewportRotationControl::_draw() {