### 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)

view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT), false);
		} break;
		case MENU_VIEW_USE_2_VIEWPORTS_ALT: {
			viewport_base->set_view(Node3DEditorViewportContainer::VIEW_USE_2_VIEWPORTS_ALT);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_1_VIEWPORT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT), true);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT), false);
		} break;
		case MENU_VIEW_USE_3_VIEWPORTS: {
			viewport_base->set_view(Node3DEditorViewportContainer::VIEW_USE_3_VIEWPORTS);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_1_VIEWPORT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS), true);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT), false);
		} break;
		case MENU_VIEW_USE_3_VIEWPORTS_ALT: {
			viewport_base->set_view(Node3DEditorViewportContainer::VIEW_USE_3_VIEWPORTS_ALT);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_1_VIEWPORT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT), false);
			view_menu->get_popup()->set_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT), true);