### 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)

}
	}
	Ref<InputEventKey> k = p_event;
	if (k.is_valid()) {
		if (!k->is_pressed()) {
			return;
		}
		if (_edit.instant) {
			
			
			
			
			bool processed = true;
			Key key = k->get_physical_keycode();
			char32_t unicode = k->get_unicode();
			if (unicode >= '0' && unicode <= '9') {
				uint32_t value = uint32_t(unicode - Key::KEY_0);
				if (_edit.numeric_next_decimal < 0) {
					_edit.numeric_input = _edit.numeric_input + value * Math::pow(10.0, _edit.numeric_next_decimal--);
				} else {
					_edit.numeric_input = _edit.numeric_input * 10 + value;
				}
				update_transform_numeric();
			} else if (unicode == '-') {
				_edit.numeric_negate = !_edit.numeric_negate;
				update_transform_numeric();
			} else if (unicode == '.') {
				if (_edit.numeric_next_decimal == 0) {
					_edit.numeric_next_decimal = -1;
				}