### 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)

return;
	}
	if (!maximized) {
		for (uint32_t i = 0; i < VIEWPORTS_COUNT; i++) {
			if (i == (uint32_t)index) {
				viewports[i]->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
			} else {
				viewports[i]->hide();
			}
		}
	} else {
		for (uint32_t i = 0; i < VIEWPORTS_COUNT; i++) {
			viewports[i]->show();
		}
		if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_1_VIEWPORT))) {
			_menu_item_pressed(MENU_VIEW_USE_1_VIEWPORT);
		} else if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS))) {
			_menu_item_pressed(MENU_VIEW_USE_2_VIEWPORTS);
		} else if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT))) {
			_menu_item_pressed(MENU_VIEW_USE_2_VIEWPORTS_ALT);
		} else if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS))) {
			_menu_item_pressed(MENU_VIEW_USE_3_VIEWPORTS);
		} else if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT))) {
			_menu_item_pressed(MENU_VIEW_USE_3_VIEWPORTS_ALT);
		} else if (view_menu->get_popup()->is_item_checked(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS))) {
			_menu_item_pressed(MENU_VIEW_USE_4_VIEWPORTS);
		}
	}
}
void Node3DEditor::_node_added(Node *p_node) {