### 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)

update_transform_numeric();
				} else {
					update_transform(Input::get_singleton()->is_key_pressed(Key::SHIFT));
				}
				accept_event();
				return;
			}
		}
		if (ED_IS_SHORTCUT("spatial_editor/snap", p_event)) {
			if (_edit.mode != TRANSFORM_NONE) {
				_edit.snap = !_edit.snap;
			}
		}
		if (ED_IS_SHORTCUT("spatial_editor/bottom_view", p_event)) {
			_menu_option(VIEW_BOTTOM);
		}
		if (ED_IS_SHORTCUT("spatial_editor/top_view", p_event)) {
			_menu_option(VIEW_TOP);
		}
		if (ED_IS_SHORTCUT("spatial_editor/rear_view", p_event)) {
			_menu_option(VIEW_REAR);
		}
		if (ED_IS_SHORTCUT("spatial_editor/front_view", p_event)) {
			_menu_option(VIEW_FRONT);
		}
		if (ED_IS_SHORTCUT("spatial_editor/left_view", p_event)) {
			_menu_option(VIEW_LEFT);
		}
		if (ED_IS_SHORTCUT("spatial_editor/right_view", p_event)) {
			_menu_option(VIEW_RIGHT);