### 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)

after = EditorPlugin::AFTER_GUI_INPUT_CUSTOM;
			}
		}
	}
	Ref<InputEventMouseButton> b = p_event;
	if (b.is_valid()) {
		emit_signal(SNAME("clicked"), this);
		const real_t zoom_factor = 1 + (ZOOM_FREELOOK_MULTIPLIER - 1) * b->get_factor();
		switch (b->get_button_index()) {
			case MouseButton::WHEEL_UP: {
				if (is_freelook_active()) {
					scale_freelook_speed(zoom_factor);
				} else {
					scale_cursor_distance(1.0 / zoom_factor);
				}
			} break;
			case MouseButton::WHEEL_DOWN: {
				if (is_freelook_active()) {
					scale_freelook_speed(1.0 / zoom_factor);
				} else {
					scale_cursor_distance(zoom_factor);
				}
			} break;
			case MouseButton::RIGHT: {
				NavigationScheme nav_scheme = (NavigationScheme)EDITOR_GET("editors/3d/navigation/navigation_scheme").operator int();
				if (b->is_pressed() && _edit.gizmo.is_valid()) {
					
					_edit.gizmo->commit_handle(_edit.gizmo_handle, _edit.gizmo_handle_secondary, _edit.gizmo_initial_value, true);
					_edit.gizmo = Ref<EditorNode3DGizmo>();
				}