### 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)

_update_gizmos_menu();
	}
	if (d.has("preview_sun_env")) {
		sun_environ_updating = true;
		Dictionary pd = d["preview_sun_env"];
		sun_rotation = pd["sun_rotation"];
		environ_sky_color->set_pick_color(pd["environ_sky_color"]);
		environ_ground_color->set_pick_color(pd["environ_ground_color"]);
		environ_energy->set_value(pd["environ_energy"]);
		environ_glow_button->set_pressed(pd["environ_glow_enabled"]);
		environ_tonemap_button->set_pressed(pd["environ_tonemap_enabled"]);
		environ_ao_button->set_pressed(pd["environ_ao_enabled"]);
		environ_gi_button->set_pressed(pd["environ_gi_enabled"]);
		sun_max_distance->set_value(pd["sun_max_distance"]);
		sun_color->set_pick_color(pd["sun_color"]);
		sun_energy->set_value(pd["sun_energy"]);
		sun_button->set_pressed(pd["sun_enabled"]);
		environ_button->set_pressed(pd["environ_enabled"]);
		sun_environ_updating = false;
		_preview_settings_changed();
		_update_preview_environment();
	} else {
		_load_default_preview_settings();
		sun_button->set_pressed(true);
		environ_button->set_pressed(true);
		_preview_settings_changed();
		_update_preview_environment();
	}
}
void Node3DEditor::edit(Node3D *p_spatial) {