### 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)

motion = Vector3(1, 0, 1);
			break;
		case TRANSFORM_YZ:
			motion = Vector3(0, 1, 1);
			break;
	}
	double value = _edit.numeric_input * (_edit.numeric_negate ? -1 : 1);
	double extra = 0.0;
	switch (_edit.mode) {
		case TRANSFORM_TRANSLATE:
			motion *= value;
			set_message(vformat(TTR("Translating %s."), motion));
			break;
		case TRANSFORM_ROTATE:
			extra = Math::deg_to_rad(value);
			set_message(vformat(TTR("Rotating %f degrees."), value));
			break;
		case TRANSFORM_SCALE:
			/
			/
			motion *= (value - 1.0);
			set_message(vformat(TTR("Scaling %s."), motion));
			break;
		case TRANSFORM_NONE:
			ERR_FAIL_MSG("_edit.mode cannot be TRANSFORM_NONE in update_transform_numeric.");
	}
	apply_transform(motion, extra);
}
/
void Node3DEditorViewport::finish_transform() {