### Godot version

v4.0.beta16.official [518b9e580]

### System information

Windows 10

### Issue description

`RichTextLabel` with `threaded` enabled may crash the game or show the following warning if the node is in another scene:

```
W 0:00:03:0802   test.gd:12 @ load_with_scene(): A Thread object has been re-started without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
  <C++ Source>   core/os/thread.cpp:76 @ start()
  <Stack Trace>  test.gd:12 @ load_with_scene()
                 test.gd:6 @ load_items()
                 test.gd:26 @ _on_button_pressed()
```

It may crash the game (without any warning) if it's added directly.

In `v4.0.beta15.official [4fa6edc88]` I was able to reproduce the same warning on my project but I can't reproduce it in the attached MRP. I get a different error and will crash too if the node is added directly:

```
E 0:00:03:0019   remove_from_group: Condition "!E" is true.
  <C++ Source>   scene/main/scene_tree.cpp:157 @ remove_from_group()
```


### Steps to reproduce

Click on the  `Load with scene` or `Load with node` buttons in the attached MRP until it shows a warning/error or crashes. It may take a while.

### Minimal reproduction project

[add_chid_bug_b16.zip](https://github.com/godotengine/godot/files/10521402/add_chid_bug_b16.zip)

msdfgen::Shape shape;
	shape.contours.clear();
	shape.inverseYAxis = false;
	MSContext context = {};
	context.shape = &shape;
	FT_Outline_Funcs ft_functions;
	ft_functions.move_to = &ft_move_to;
	ft_functions.line_to = &ft_line_to;
	ft_functions.conic_to = &ft_conic_to;
	ft_functions.cubic_to = &ft_cubic_to;
	ft_functions.shift = 0;
	ft_functions.delta = 0;
	int error = FT_Outline_Decompose(outline, &ft_functions, &context);
	ERR_FAIL_COND_V_MSG(error, FontGlyph(), "FreeType: Outline decomposition error: '" + String(FT_Error_String(error)) + "'.");
	if (!shape.contours.empty() && shape.contours.back().edges.empty()) {
		shape.contours.pop_back();
	}
	if (FT_Outline_Get_Orientation(outline) == 1) {
		for (int i = 0; i < (int)shape.contours.size(); ++i) {
			shape.contours[i].reverse();
		}
	}
	shape.inverseYAxis = true;
	shape.normalize();
	msdfgen::Shape::Bounds bounds = shape.getBounds(p_pixel_range);