box.schema.user.disable('admin') reports an obscure error

```lua
$ tarantool -i
Tarantool 3.4.0-entrypoint-279-ge57fc4c71
type 'help' for interactive help
tarantool> box.cfg()
tarantool> box.schema.user.disable('admin')
---
- error: 'Tuple field 5 (privilege) type does not match one required by operation:
    expected unsigned, got integer'
...
```

If this operation is forbidden, it would be nice to get a clear error.