### 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)

ccpert("ccp_BD"));
		ccpert("ccp_IN"));
		ccp.digits = U"𑄶𑄷𑄸𑄹𑄺𑄻𑄼𑄽𑄾𑄿.";
		ccpsign = U"%";
		ccp.exp = U"e";
		num_systems.push_back(ccp);
	}
	// Adlam numerals.
	{
		NumSystemData ff;
		ffert("ff")); // Fulah
		ffert("ff_Adlm_BF"));
		ffert
		ffert("ff_Adlm_GH"));
		ffert("ff_Adlm_GM"));
		ffert("ff_Adlm_GN"));
		ffert("ff_Adlm_GW"));
		ffert("ff_Adlm_LR"));
		ffert("ff_Adlm_MR"));
		ffert("ff_Adlm_NE"));
		ffert("ff_Adlm_NG"));
		ffert("ff_Adlm_SL"));
		ffert("ff_Adlm_SN"));
		ff.digits = U"𞥐𞥑𞥒𞥓𞥔𞥕𞥖𞥗𞥘𞥙.";
		ffsign = U"%";
		ff.exp = U"e";
		num_systems.push_back(ff);
	}
}
String TextServerAdvanced::_format_number(const String &p_string, const String &p_language) const {