### 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.
downgrades_assigned = !assigned_is_hard;
		}
	}
	p_assignment->set_datatype(op_type);
	if (assignee_is_variant) {
		if (!assignee_is_hard) {
			
			mark_node_unsafe(p_assignment);
		}
	} else {
		if (assignee_is_hard && !assigned_is_hard) {
			
			mark_node_unsafe(p_assignment);
			p_assignment->use_conversion_assign = true;
			downgrades_assigned = downgrades_assigned || (!assigned_is_variant && !is_type_compatible(assignee_type, op_type, true, p_assignment->assigned_value));
		} else if (compatible) {
			if (op_type.is_variant()) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {
					
					p_assignment->use_conversion_assign = true;
				} else {
					
					downgrades_assignee = true;
				}
			} else if (!is_type_compatible(assignee_type, op_type, assignee_is_hard, p_assignment->assigned_value)) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {