### Godot version

v4.1.1.stable.official [bd6af8e0e]

### System information

Windows 10

### Issue description

As said in the Title Custom Class Documentation a Function cannot return 'Variant' and will instead be shown to return void, even though Built-in Classes are shown to return 'Variant', an example would be 'Array'
![image](https://github.com/godotengine/godot/assets/34311843/fb8ad532-c37a-43c0-a95f-d70af7ea6894)
![image](https://github.com/godotengine/godot/assets/34311843/3cc1e07b-02e1-4f33-bc98-0fa016b4d864)

### Steps to reproduce

```gdscript
extends Node
class_name CustomClass

func VariantFunction() -> Variant:
	return 10
``` 
Now when checking the Generated Documentation it will appear like: `void VariantFunction()`

### Minimal reproduction project

N/A
p_script->_clear_doc();
	DocData::ClassDoc &doc = p_script->doc;
	doc.script_path = _get_script_path(p_script->get_script_path());
	if (p_script->name.is_empty()) {
		doc.name = doc.script_path;
	} else {
		doc.name = p_script->name;
	}
	if (p_script->_owner) {
		doc.name = p_script->_owner->doc.name + "." + doc.name;
		doc.script_path = doc.script_path + "." + doc.name;
	}
	doc.is_script_doc = true;
	if (p_script->base.is_valid() && p_script->base->is_valid()) {
		if (!p_script->base->doc.name.is_empty()) {
			doc.inherits = p_script->base->doc.name;
		} else {
			doc.inherits = p_script->base->get_instance_base_type();
		}
	} else if (p_script->native.is_valid()) {
		doc.inherits = p_script->native->get_name();
	}
	doc.brief_description = p_class->doc_data.brief;
	doc.description = p_class->doc_data.description;
	for (const Pair<String, String> &p : p_class->doc_data.tutorials) {
		DocData::TutorialDoc td;
		td.title = p.first;
		td.link = p.second;