### Godot version

Beta 17, master

### System information

Windows 11

### Issue description

Godot gets a hard crash while attempting to code-complete for member `const` of a class.

### Steps to reproduce

```GDScript
enum E { V1 }

const e := E
```

And then type a `.` after the last `E`, which triggers code hints/auto-completion for subscripts based on `E` and causes a hard crash.

Does not happen for `var e := E.V1`.

### Minimal reproduction project

See above.
reduce_expression(p_assignment->assignee);
	reduce_expression(p_assignment->assigned_value);
	if (p_assignment->assigned_value == nullptr || p_assignment->assignee == nullptr) {
		return;
	}
	GDScriptParser::DataType assignee_type = p_assignment->assignee->get_datatype();
	if (assignee_type.is_constant || (p_assignment->assignee->type == GDScriptParser::Node::SUBSCRIPT && static_cast<GDScriptParser::SubscriptNode *>(p_assignment->assignee)->base->is_constant)) {
		push_error("Cannot assign a new value to a constant.", p_assignment->assignee);
	}
	
	if (p_assignment->assigned_value->type == GDScriptParser::Node::ARRAY && assignee_type.has_container_element_type()) {
		update_array_literal_element_type(static_cast<GDScriptParser::ArrayNode *>(p_assignment->assigned_value), assignee_type.get_container_element_type());
	}