we only need to support `asc` and `ASC`. No need for mixed cases. #14263

This is a result of the discussion at https://github.com/rails/rails/pull/14263/files#r10291489
get rid of intermediate arrays.

origin: https://github.com/rails/rails/commit/f6aeb8b1a3687c8523e4a56309fe3736011b2935#commitcomment-5569649
Remove a reference to an issue [ci skip]

This actually not an issue fixing ; the changelog is referring to the
introducing pull request itself.