### 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)

FT_Outline_Embolden(&fd->face->glyph->outline, strength);
		}
		if (p_font_data->transform != Transform2D()) {
			FT_Matrix mat = { FT_Fixed(p_font_data->transform[0][0] * 65536), FT_Fixed(p_font_data->transform[0][1] * 65536), FT_Fixed(p_font_data->transform[1][0] * 65536), FT_Fixed(p_font_data->transform[1][1] * 65536) }; 
			FT_Outline_Transform(&fd->face->glyph->outline, &mat);
		}
		FT_Render_Mode aa_mode = FT_RENDER_MODE_NORMAL;
		bool bgra = false;
		switch (p_font_data->antialiasing) {
			case FONT_ANTIALIASING_NONE: {
				aa_mode = FT_RENDER_MODE_MONO;
			} 
			case FONT_ANTIALIASING_GRAY: {
				aa_mode = FT_RENDER_MODE_NORMAL;
			} 
			case FONT_ANTIALIASING_LCD: {
				int aa_layout = (int)((p_glyph >> 24) & 7);
				switch (aa_layout) {
					case FONT_LCD_SUBPIXEL_LAYOUT_HRGB: {
						aa_mode = FT_RENDER_MODE_LCD;
						bgra = false;
					} 
					case FONT_LCD_SUBPIXEL_LAYOUT_HBGR: {
						aa_mode = FT_RENDER_MODE_LCD;
						bgra = true;
					} 
					case FONT_LCD_SUBPIXEL_LAYOUT_VRGB: {
						aa_mode = FT_RENDER_MODE_LCD_V;
						bgra = false;
					}