### 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)

char32_t c = sd->text[pos_p];
					if (pos - sd->start != sd->end && !is_whitespace(c) && (c != 0xfffc)) {
						sd->break_inserts++;
					}
				}
			}
			ubrk_close(bi);
			i++;
		}
		sd->break_ops_valid = true;
	}
	Vector<Glyph> glyphs_new;
	bool rewrite = false;
	int sd_shift = 0;
	int sd_size = sd->glyphs.size();
	Glyph *sd_glyphs = sd->glyphs.ptrw();
	Glyph *sd_glyphs_new = nullptr;
	if (sd->break_inserts > 0) {
		glyphs_new.resize(sd->glyphs.size() + sd->break_inserts);
		sd_glyphs_new = glyphs_new.ptrw();
		rewrite = true;
	} else {
		sd_glyphs_new = sd_glyphs;
	}
	sd->sort_valid = false;
	sd->glyphs_logical.clear();
	const char32_t *ch = sd->text.ptr();
	int c_punct_size = sd->custom_punct.length();
	const char32_t *c_punct = sd->custom_punct.ptr();
	for (int i = 0; i < sd_size; i++) {