### 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
doc.tutorials.append(td);
	}
	doc.is_deprecated = p_class->doc_data.is_deprecated;
	doc.is_experimental = p_class->doc_data.is_experimental;
	for (const GDP::ClassNode::Member &member : p_class->members) {
		switch (member.type) {
			case GDP::ClassNode::Member::CLASS: {
				const GDP::ClassNode *inner_class = member.m_class;
				const StringName &class_name = inner_class->identifier->name;
				p_script->member_lines[class_name] = inner_class->start_line;
				
				
				GDScriptDocGen::generate_docs(*p_script->subclasses[class_name], inner_class);
			} break;
			case GDP::ClassNode::Member::CONSTANT: {
				const GDP::ConstantNode *m_const = member.constant;
				const StringName &const_name = member.constant->identifier->name;
				p_script->member_lines[const_name] = m_const->start_line;
				DocData::ConstantDoc const_doc;
				DocData::constant_doc_from_variant(const_doc, const_name, m_const->initializer->reduced_value, m_const->doc_data.description);
				const_doc.is_deprecated = m_const->doc_data.is_deprecated;
				const_doc.is_experimental = m_const->doc_data.is_experimental;
				doc.constants.push_back(const_doc);
			} break;
			case GDP::ClassNode::Member::FUNCTION: {
				const GDP::FunctionNode *m_func = member.function;
				const StringName &func_name = m_func->identifier->name;
				p_script->member_lines[func_name] = m_func->start_line;
				MethodInfo mi;
				mi.name = func_name;