### 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
const_doc.value = String(Variant(val.value));
					const_doc.is_value_valid = true;
					const_doc.enumeration = name;
					const_doc.description = val.doc_data.description;
					const_doc.is_deprecated = val.doc_data.is_deprecated;
					const_doc.is_experimental = val.doc_data.is_experimental;
					doc.constants.push_back(const_doc);
				}
			} break;
			case GDP::ClassNode::Member::ENUM_VALUE: {
				const GDP::EnumNode::Value &m_enum_val = member.enum_value;
				const StringName &name = m_enum_val.identifier->name;
				p_script->member_lines[name] = m_enum_val.identifier->start_line;
				DocData::ConstantDoc const_doc;
				DocData::constant_doc_from_variant(const_doc, name, m_enum_val.value, m_enum_val.doc_data.description);
				const_doc.enumeration = "@unnamed_enums";
				const_doc.is_deprecated = m_enum_val.doc_data.is_deprecated;
				const_doc.is_experimental = m_enum_val.doc_data.is_experimental;
				doc.constants.push_back(const_doc);
			} break;
			case GDP::ClassNode::Member::GROUP:
			case GDP::ClassNode::Member::UNDEFINED:
			default:
				break;
		}
	}
	
	p_script->_add_doc(doc);
}