### Godot version

4.1.1

### System information

windows 11

### Issue description

When registering a type with class_name and using that class name to declare a variable in code only, autocomplete works as expected anywhere in other nodes/scenes. However, if making a custom scene node that extends a script with the class_name, if that custom scene is instantiated in a different scene, even if the type is specified, it only shows the parent node's functions and not any of the extended functionality. I have made a basic project showing the issue

### Steps to reproduce

I have made a very simple project showing the issue. https://github.com/mmmmmmmmmmmmmmmmmmmdonuts/godot_4_autocomplete_issue essentially, the extended Node scene will only show the custom function when both the type is specified as well as the type afterwards following "as" 
e.g. `@onready var my_class_4: MyClass = $MyClass4 as MyClass`

### Minimal reproduction project

https://github.com/mmmmmmmmmmmmmmmmmmmdonuts/godot_4_autocomplete_issue
}
			if (_lookup_symbol_from_base(base.type, p_symbol, is_function, r_result) == OK) {
				return OK;
			}
		} break;
		case GDScriptParser::COMPLETION_TYPE_ATTRIBUTE: {
			if (context.node == nullptr || context.node->type != GDScriptParser::Node::TYPE) {
				break;
			}
			const GDScriptParser::TypeNode *type = static_cast<const GDScriptParser::TypeNode *>(context.node);
			GDScriptParser::DataType base_type;
			const GDScriptParser::IdentifierNode *prev = nullptr;
			for (const GDScriptParser::IdentifierNode *E : type->type_chain) {
				if (E->name == p_symbol && prev != nullptr) {
					base_type = prev->get_datatype();
					break;
				}
				prev = E;
			}
			if (base_type.kind != GDScriptParser::DataType::CLASS) {
				GDScriptCompletionIdentifier base;
				if (!_guess_expression_type(context, prev, base)) {
					break;
				}
				base_type = base.type;
			}
			if (_lookup_symbol_from_base(base_type, p_symbol, is_function, r_result) == OK) {
				return OK;
			}
		} break;