### 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)

sun_vb->show();
			preview_sun_dangling = false;
		}
	}
	sun_angle_altitude->set_value(-Math::rad_to_deg(sun_rotation.x));
	sun_angle_azimuth->set_value(180.0 - Math::rad_to_deg(sun_rotation.y));
	bool disable_env = world_env_count > 0 || !environ_button->is_pressed();
	environ_button->set_disabled(world_env_count > 0);
	if (disable_env) {
		if (preview_environment->get_parent()) {
			preview_environment->get_parent()->remove_child(preview_environment);
			environ_state->show();
			environ_vb->hide();
			preview_env_dangling = true;
		}
		if (world_env_count > 0) {
			environ_state->set_text(TTR("Scene contains\nWorldEnvironment.\nPreview disabled."));
		} else {
			environ_state->set_text(TTR("Preview disabled."));
		}
	} else {
		if (!preview_environment->get_parent()) {
			add_child(preview_environment);
			environ_state->hide();
			environ_vb->show();
			preview_env_dangling = false;
		}
	}
}
void Node3DEditor::_sun_direction_input(const Ref<InputEvent> &p_event) {