### 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)

fc->set_variation_embolden(emb);
					} else if (subtag_a[0] == "face_index" || subtag_a[0] == "fi") {
						int fi = subtag_a[1].to_int();
						fc->set_variation_face_index(fi);
					} else if (subtag_a[0] == "slant" || subtag_a[0] == "sln") {
						float slant = subtag_a[1].to_float();
						fc->set_variation_transform(Transform2D(1.0, slant, 0.0, 1.0, 0.0, 0.0));
					} else if (subtag_a[0] == "opentype_variation" || subtag_a[0] == "otv") {
						Dictionary variations;
						if (!subtag_a[1].is_empty()) {
							Vector<String> variation_tags = subtag_a[1].split(",");
							for (int j = 0; j < variation_tags.size(); j++) {
								Vector<String> subtag_b = variation_tags[j].split("=");
								if (subtag_b.size() == 2) {
									variations[TS->name_to_tag(subtag_b[0])] = subtag_b[1].to_float();
								}
							}
							fc->set_variation_opentype(variations);
						}
					} else if (subtag_a[0] == "opentype_features" || subtag_a[0] == "otf") {
						Dictionary features;
						if (!subtag_a[1].is_empty()) {
							Vector<String> feature_tags = subtag_a[1].split(",");
							for (int j = 0; j < feature_tags.size(); j++) {
								Vector<String> subtag_b = feature_tags[j].split("=");
								if (subtag_b.size() == 2) {
									features[TS->name_to_tag(subtag_b[0])] = subtag_b[1].to_float();
								} else if (subtag_b.size() == 1) {
									features[TS->name_to_tag(subtag_b[0])] = 1;
								}