### 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)

}
			if (preview_node->is_inside_tree()) {
				preview_node_pos = spatial_editor->snap_point(_get_instance_position(preview_node_viewport_pos));
				Transform3D preview_gl_transform = Transform3D(Basis(), preview_node_pos);
				preview_node->set_global_transform(preview_gl_transform);
				if (!preview_node->is_visible()) {
					preview_node->show();
				}
			}
			update_preview_node = false;
		} break;
		case NOTIFICATION_ENTER_TREE: {
			surface->connect("draw", callable_mp(this, &Node3DEditorViewport::_draw));
			surface->connect("gui_input", callable_mp(this, &Node3DEditorViewport::_sinput));
			surface->connect("mouse_entered", callable_mp(this, &Node3DEditorViewport::_surface_mouse_enter));
			surface->connect("mouse_exited", callable_mp(this, &Node3DEditorViewport::_surface_mouse_exit));
			surface->connect("focus_entered", callable_mp(this, &Node3DEditorViewport::_surface_focus_enter));
			surface->connect("focus_exited", callable_mp(this, &Node3DEditorViewport::_surface_focus_exit));
			_init_gizmo_instance(index);
		} break;
		case NOTIFICATION_EXIT_TREE: {
			_finish_gizmo_instances();
		} break;
		case NOTIFICATION_THEME_CHANGED: {
			view_menu->set_icon(get_editor_theme_icon(SNAME("GuiTabMenuHl")));
			preview_camera->set_icon(get_editor_theme_icon(SNAME("Camera3D")));
			Control *gui_base = EditorNode::get_singleton()->get_gui_base();
			view_menu->begin_bulk_theme_override();
			view_menu->add_theme_style_override("normal", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));
			view_menu->add_theme_style_override("hover", gui_base->get_theme_stylebox(SNAME("Information3dViewport"), EditorStringName(EditorStyles)));