### 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)

viewports[i]->hide();
						} else {
							viewports[i]->show();
						}
					}
					fit_child_in_rect(viewports[0], Rect2(Vector2(), Vector2(size_left, size_top)));
					fit_child_in_rect(viewports[2], Rect2(Vector2(0, mid_h + v_sep / 2), Vector2(size_left, size_bottom)));
					fit_child_in_rect(viewports[3], Rect2(Vector2(mid_w + h_sep / 2, 0), Vector2(size_right, size.height)));
				} break;
				case VIEW_USE_4_VIEWPORTS: {
					for (int i = 0; i < 4; i++) {
						viewports[i]->show();
					}
					fit_child_in_rect(viewports[0], Rect2(Vector2(), Vector2(size_left, size_top)));
					fit_child_in_rect(viewports[1], Rect2(Vector2(mid_w + h_sep / 2, 0), Vector2(size_right, size_top)));
					fit_child_in_rect(viewports[2], Rect2(Vector2(0, mid_h + v_sep / 2), Vector2(size_left, size_bottom)));
					fit_child_in_rect(viewports[3], Rect2(Vector2(mid_w + h_sep / 2, mid_h + v_sep / 2), Vector2(size_right, size_bottom)));
				} break;
			}
		} break;
	}
}
void Node3DEditorViewportContainer::set_view(View p_view) {
	view = p_view;
	queue_sort();
}
Node3DEditorViewportContainer::View Node3DEditorViewportContainer::get_view() {
	return view;
}
Node3DEditorViewportContainer::Node3DEditorViewportContainer() {