### 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)

} else {
						continue;
					}
					can_instantiate = true;
					break;
				}
			}
			if (can_instantiate) {
				_create_preview_node(files);
				preview_node->hide();
			}
		}
	} else {
		if (preview_node->is_inside_tree()) {
			can_instantiate = true;
		}
	}
	if (can_instantiate) {
		update_preview_node = true;
		return true;
	}
	if (spatial_editor->get_preview_material().is_valid()) {
		preview_material_label->show();
		preview_material_label_desc->show();
		ObjectID new_preview_material_target = _select_ray(p_point);
		return _apply_preview_material(new_preview_material_target, p_point);
	}
	return false;
}
void Node3DEditorViewport::drop_data_fw(const Point2 &p_point, const Variant &p_data, Control *p_from) {