### 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)

void push_bold();
	void push_bold_italics();
	void push_italics();
	void push_mono();
	void push_color(const Color &p_color);
	void push_outline_color(const Color &p_color);
	void push_underline();
	void push_strikethrough();
	void push_paragraph(HorizontalAlignment p_alignment, Control::TextDirection p_direction = Control::TEXT_DIRECTION_INHERITED, const String &p_language = "", TextServer::StructuredTextParser p_st_parser = TextServer::STRUCTURED_TEXT_DEFAULT);
	void push_indent(int p_level);
	void push_list(int p_level, ListType p_list, bool p_capitalize);
	void push_meta(const Variant &p_meta);
	void push_hint(const String &p_string);
	void push_table(int p_columns, InlineAlignment p_alignment = INLINE_ALIGNMENT_TOP, int p_align_to_row = -1);
	void push_fade(int p_start_index, int p_length);
	void push_shake(int p_strength, float p_rate, bool p_connected);
	void push_wave(float p_frequency, float p_amplitude, bool p_connected);
	void push_tornado(float p_frequency, float p_radius, bool p_connected);
	void push_rainbow(float p_saturation, float p_value, float p_frequency);
	void push_bgcolor(const Color &p_color);
	void push_fgcolor(const Color &p_color);
	void push_customfx(Ref<RichTextEffect> p_custom_effect, Dictionary p_environment);
	void set_table_column_expand(int p_column, bool p_expand, int p_ratio = 1);
	void set_cell_row_background_color(const Color &p_odd_row_bg, const Color &p_even_row_bg);
	void set_cell_border_color(const Color &p_color);
	void set_cell_size_override(const Size2 &p_min_size, const Size2 &p_max_size);
	void set_cell_padding(const Rect2 &p_padding);
	int get_current_table_column() const;
	void push_cell();
	void pop();