### 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.
if (p_assignment->operation == GDScriptParser::AssignmentNode::OP_NONE && assignee_type.is_hard_type() && p_assignment->assigned_value->is_constant) {
		update_const_expression_builtin_type(p_assignment->assigned_value, assignee_type, "assign");
	}
	GDScriptParser::DataType assigned_value_type = p_assignment->assigned_value->get_datatype();
	bool assignee_is_variant = assignee_type.is_variant();
	bool assignee_is_hard = assignee_type.is_hard_type();
	bool assigned_is_variant = assigned_value_type.is_variant();
	bool assigned_is_hard = assigned_value_type.is_hard_type();
	bool compatible = true;
	bool downgrades_assignee = false;
	bool downgrades_assigned = false;
	GDScriptParser::DataType op_type = assigned_value_type;
	if (p_assignment->operation != GDScriptParser::AssignmentNode::OP_NONE && !op_type.is_variant()) {
		op_type = get_operation_type(p_assignment->variant_op, assignee_type, assigned_value_type, compatible, p_assignment->assigned_value);
		if (assignee_is_variant) {
			
			mark_node_unsafe(p_assignment);
		} else if (!compatible) {
			
			mark_node_unsafe(p_assignment);
			if (assigned_is_variant) {
				
				p_assignment->use_conversion_assign = true;
			} else {
				
				push_error(vformat(R"(Invalid operands "%s" and "%s" for assignment operator.)", assignee_type.to_string(), assigned_value_type.to_string()), p_assignment);
			}
		} else if (op_type.type_source == GDScriptParser::DataType::UNDETECTED && !assigned_is_variant) {
			
			downgrades_assignee = !assignee_is_hard;