For now, the target attribute allows attribute aliases, but `:scope`'s
attribute does not, the cause is that the former use
`read_attribute_for_validation`, but the latter does not.

Unfortunately we cannot use `read_attribute_for_validation` in this
case, it intentionally bypass custom attribute getter to allow #7072.

To work both alias and #7072, `read_attribute` should be used to resolve
attribute aliases.