### 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->add_theme_style_override("pressed", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			view_menu->add_theme_style_override("focus", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			view_menu->add_theme_style_override("disabled", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			view_menu->end_bulk_theme_override();
			preview_camera->begin_bulk_theme_override();
			preview_camera->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			preview_camera->add_theme_style_override("hover", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			preview_camera->add_theme_style_override("pressed", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			preview_camera->add_theme_style_override("focus", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			preview_camera->add_theme_style_override("disabled", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			preview_camera->end_bulk_theme_override();
			frame_time_gradient->set_color(0, get_theme_color(SNAME("success_color"), EditorStringName(Editor)));
			frame_time_gradient->set_color(1, get_theme_color(SNAME("warning_color"), EditorStringName(Editor)));
			frame_time_gradient->set_color(2, get_theme_color(SNAME("error_color"), EditorStringName(Editor)));
			info_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			cpu_time_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			gpu_time_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			fps_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			cinema_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			locked_label->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
		} break;
		case NOTIFICATION_DRAG_END: {
			/
			if (spatial_editor->get_preview_material().is_valid() && !is_drag_successful()) {
				_remove_preview_material();
			}
		} break;
	}
}
static void draw_indicator_bar(Control &p_surface, real_t p_fill, const Ref<Texture2D> p_icon, const Ref<Font> p_font, int p_font_size, const String &p_text, const Color &p_color) {