### 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)

tool_button[TOOL_MODE_SELECT]->set_icon(get_editor_theme_icon(SNAME("ToolSelect")));
	tool_button[TOOL_MODE_MOVE]->set_icon(get_editor_theme_icon(SNAME("ToolMove")));
	tool_button[TOOL_MODE_ROTATE]->set_icon(get_editor_theme_icon(SNAME("ToolRotate")));
	tool_button[TOOL_MODE_SCALE]->set_icon(get_editor_theme_icon(SNAME("ToolScale")));
	tool_button[TOOL_MODE_LIST_SELECT]->set_icon(get_editor_theme_icon(SNAME("ListSelect")));
	tool_button[TOOL_LOCK_SELECTED]->set_icon(get_editor_theme_icon(SNAME("Lock")));
	tool_button[TOOL_UNLOCK_SELECTED]->set_icon(get_editor_theme_icon(SNAME("Unlock")));
	tool_button[TOOL_GROUP_SELECTED]->set_icon(get_editor_theme_icon(SNAME("Group")));
	tool_button[TOOL_UNGROUP_SELECTED]->set_icon(get_editor_theme_icon(SNAME("Ungroup")));
	tool_option_button[TOOL_OPT_LOCAL_COORDS]->set_icon(get_editor_theme_icon(SNAME("Object")));
	tool_option_button[TOOL_OPT_USE_SNAP]->set_icon(get_editor_theme_icon(SNAME("Snap")));
	tool_option_button[TOOL_OPT_OVERRIDE_CAMERA]->set_icon(get_editor_theme_icon(SNAME("Camera3D")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_1_VIEWPORT), get_editor_theme_icon(SNAME("Panels1")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS), get_editor_theme_icon(SNAME("Panels2")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_2_VIEWPORTS_ALT), get_editor_theme_icon(SNAME("Panels2Alt")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS), get_editor_theme_icon(SNAME("Panels3")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_3_VIEWPORTS_ALT), get_editor_theme_icon(SNAME("Panels3Alt")));
	view_menu->get_popup()->set_item_icon(view_menu->get_popup()->get_item_index(MENU_VIEW_USE_4_VIEWPORTS), get_editor_theme_icon(SNAME("Panels4")));
	sun_button->set_icon(get_editor_theme_icon(SNAME("PreviewSun")));
	environ_button->set_icon(get_editor_theme_icon(SNAME("PreviewEnvironment")));
	sun_environ_settings->set_icon(get_editor_theme_icon(SNAME("GuiTabMenuHl")));
	sun_title->add_theme_font_override("font", get_theme_font(SNAME("title_font"), SNAME("Window")));
	environ_title->add_theme_font_override("font", get_theme_font(SNAME("title_font"), SNAME("Window")));
	sun_color->set_custom_minimum_size(Size2(0, get_theme_constant(SNAME("color_picker_button_height"), EditorStringName(Editor))));
	environ_sky_color->set_custom_minimum_size(Size2(0, get_theme_constant(SNAME("color_picker_button_height"), EditorStringName(Editor))));
	environ_ground_color->set_custom_minimum_size(Size2(0, get_theme_constant(SNAME("color_picker_button_height"), EditorStringName(Editor))));
	context_toolbar_panel->add_theme_style_override("panel", get_theme_stylebox(SNAME("ContextualToolbar"), EditorStringName(EditorStyles)));
}
void Node3DEditor::_notification(int p_what) {