### 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)

set_clip_contents(true);
	view = VIEW_USE_1_VIEWPORT;
	mouseover = false;
	ratio_h = 0.5;
	ratio_v = 0.5;
	hovering_v = false;
	hovering_h = false;
	dragging_v = false;
	dragging_h = false;
}
/
Node3DEditor *Node3DEditor::singleton = nullptr;
Node3DEditorSelectedItem::~Node3DEditorSelectedItem() {
	ERR_FAIL_NULL(RenderingServer::get_singleton());
	if (sbox_instance.is_valid()) {
		RenderingServer::get_singleton()->free(sbox_instance);
	}
	if (sbox_instance_offset.is_valid()) {
		RenderingServer::get_singleton()->free(sbox_instance_offset);
	}
	if (sbox_instance_xray.is_valid()) {
		RenderingServer::get_singleton()->free(sbox_instance_xray);
	}
	if (sbox_instance_xray_offset.is_valid()) {
		RenderingServer::get_singleton()->free(sbox_instance_xray_offset);
	}
}
void Node3DEditor::select_gizmo_highlight_axis(int p_axis) {