### 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
return OK;
					}
				} else {
					List<StringName> utility_functions;
					Variant::get_utility_function_list(&utility_functions);
					if (utility_functions.find(p_symbol) != nullptr) {
						r_result.type = ScriptLanguage::LOOKUP_RESULT_CLASS_TBD_GLOBALSCOPE;
						r_result.class_name = "@GlobalScope";
						r_result.class_member = p_symbol;
						return OK;
					}
				}
			}
		} break;
		case GDScriptParser::COMPLETION_ATTRIBUTE_METHOD: {
			is_function = true;
			[[fallthrough]];
		}
		case GDScriptParser::COMPLETION_ATTRIBUTE: {
			if (context.node->type != GDScriptParser::Node::SUBSCRIPT) {
				break;
			}
			const GDScriptParser::SubscriptNode *subscript = static_cast<const GDScriptParser::SubscriptNode *>(context.node);
			if (!subscript->is_attribute) {
				break;
			}
			GDScriptCompletionIdentifier base;
			bool found_type = _get_subscript_type(context, subscript, base.type);
			if (!found_type && !_guess_expression_type(context, subscript->base, base)) {
				break;