### 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)

environ_add_to_scene->connect("pressed", callable_mp(this, &Node3DEditor::_add_environment_to_scene).bind(false));
		environ_vb->add_spacer();
		environ_vb->add_child(environ_add_to_scene);
		environ_state = memnew(Label);
		sun_environ_hb->add_child(environ_state);
		environ_state->set_horizontal_alignment(HORIZONTAL_ALIGNMENT_CENTER);
		environ_state->set_vertical_alignment(VERTICAL_ALIGNMENT_CENTER);
		environ_state->set_h_size_flags(SIZE_EXPAND_FILL);
		preview_sun = memnew(DirectionalLight3D);
		preview_sun->set_shadow(true);
		preview_sun->set_shadow_mode(DirectionalLight3D::SHADOW_PARALLEL_4_SPLITS);
		preview_environment = memnew(WorldEnvironment);
		environment.instantiate();
		preview_environment->set_environment(environment);
		if (GLOBAL_GET("rendering/lights_and_shadows/use_physical_light_units")) {
			camera_attributes.instantiate();
			preview_environment->set_camera_attributes(camera_attributes);
		}
		Ref<Sky> sky;
		sky.instantiate();
		sky_material.instantiate();
		sky->set_material(sky_material);
		environment->set_sky(sky);
		environment->set_background(Environment::BG_SKY);
		_load_default_preview_settings();
		_preview_settings_changed();
	}
	clear(); /
}
Node3DEditor::~Node3DEditor() {