### 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)

if (b->is_pressed() && _edit.mode != TRANSFORM_NONE) {
					switch (_edit.plane) {
						case TRANSFORM_VIEW: {
							_edit.plane = TRANSFORM_X_AXIS;
							set_message(TTR("X-Axis Transform."), 2);
							view_type = VIEW_TYPE_USER;
							_update_name();
						} break;
						case TRANSFORM_X_AXIS: {
							_edit.plane = TRANSFORM_Y_AXIS;
							set_message(TTR("Y-Axis Transform."), 2);
						} break;
						case TRANSFORM_Y_AXIS: {
							_edit.plane = TRANSFORM_Z_AXIS;
							set_message(TTR("Z-Axis Transform."), 2);
						} break;
						case TRANSFORM_Z_AXIS: {
							_edit.plane = TRANSFORM_VIEW;
							
							set_message(TTR("View Plane Transform."), 2);
						} break;
						case TRANSFORM_YZ:
						case TRANSFORM_XZ:
						case TRANSFORM_XY: {
						} break;
					}
				}
			} break;
			case MouseButton::LEFT: {
				if (b->is_pressed()) {