### 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)

continue;
							}
							int gizmo_handle = -1;
							bool gizmo_secondary = false;
							seg->handles_intersect_ray(camera, _edit.mouse_pos, b->is_shift_pressed(), gizmo_handle, gizmo_secondary);
							if (gizmo_handle != -1) {
								_edit.gizmo = seg;
								seg->begin_handle_action(gizmo_handle, gizmo_secondary);
								_edit.gizmo_handle = gizmo_handle;
								_edit.gizmo_handle_secondary = gizmo_secondary;
								_edit.gizmo_initial_value = seg->get_handle_value(gizmo_handle, gizmo_secondary);
								intersected_handle = true;
								break;
							}
						}
						if (intersected_handle) {
							break;
						}
					}
					
					if (_transform_gizmo_select(_edit.mouse_pos)) {
						break;
					}
					
					if (can_select_gizmos) {
						Node3DEditorSelectedItem *se = editor_selection->get_node_editor_data<Node3DEditorSelectedItem>(spatial_editor->get_single_selected_node());
						Vector<Ref<Node3DGizmo>> gizmos = spatial_editor->get_single_selected_node()->get_gizmos();
						bool intersected_subgizmo = false;
						for (int i = 0; i < gizmos.size(); i++) {
							Ref<EditorNode3DGizmo> seg = gizmos[i];