### 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)

flags |= FT_LOAD_TARGET_NORMAL;
				
		}
		if (p_font_data->force_autohinter) {
			flags |= FT_LOAD_FORCE_AUTOHINT;
		}
		if (outline) {
			flags |= FT_LOAD_NO_BITMAP;
		} else if (FT_HAS_COLOR(fd->face)) {
			flags |= FT_LOAD_COLOR;
		}
		FT_Fixed v, h;
		FT_Get_Advance(fd->face, glyph_index, flags, &h);
		FT_Get_Advance(fd->face, glyph_index, flags | FT_LOAD_VERTICAL_LAYOUT, &v);
		int error = FT_Load_Glyph(fd->face, glyph_index, flags);
		if (error) {
			fd->glyph_map[p_glyph] = FontGlyph();
			return false;
		}
		if (!p_font_data->msdf) {
			if ((p_font_data->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_QUARTER) || (p_font_data->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && p_size.x <= SUBPIXEL_POSITIONING_ONE_QUARTER_MAX_SIZE)) {
				FT_Pos xshift = (int)((p_glyph >> 27) & 3) << 4;
				FT_Outline_Translate(&fd->face->glyph->outline, xshift, 0);
			} else if ((p_font_data->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_HALF) || (p_font_data->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && p_size.x <= SUBPIXEL_POSITIONING_ONE_HALF_MAX_SIZE)) {
				FT_Pos xshift = (int)((p_glyph >> 27) & 3) << 5;
				FT_Outline_Translate(&fd->face->glyph->outline, xshift, 0);
			}
		}
		if (p_font_data->embolden != 0.f) {
			FT_Pos strength = p_font_data->embolden * p_size.x * 4;