### 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)

Viewport::DEBUG_DRAW_PSSM_SPLITS,
				Viewport::DEBUG_DRAW_DECAL_ATLAS,
				Viewport::DEBUG_DRAW_SDFGI,
				Viewport::DEBUG_DRAW_SDFGI_PROBES,
				Viewport::DEBUG_DRAW_CLUSTER_OMNI_LIGHTS,
				Viewport::DEBUG_DRAW_CLUSTER_SPOT_LIGHTS,
				Viewport::DEBUG_DRAW_CLUSTER_DECALS,
				Viewport::DEBUG_DRAW_CLUSTER_REFLECTION_PROBES,
				Viewport::DEBUG_DRAW_OCCLUDERS,
				Viewport::DEBUG_DRAW_MOTION_VECTORS,
				Viewport::DEBUG_DRAW_INTERNAL_BUFFER,
			};
			for (int idx = 0; display_options[idx] != VIEW_MAX; idx++) {
				int id = display_options[idx];
				int item_idx = view_menu->get_popup()->get_item_index(id);
				if (item_idx != -1) {
					view_menu->get_popup()->set_item_checked(item_idx, id == p_option);
				}
				item_idx = display_submenu->get_item_index(id);
				if (item_idx != -1) {
					display_submenu->set_item_checked(item_idx, id == p_option);
				}
				if (id == p_option) {
					viewport->set_debug_draw(debug_draw_modes[idx]);
				}
			}
		} break;
	}
}
void Node3DEditorViewport::_set_auto_orthogonal() {