Fixed #22711 -- Allow model's Meta.ordering attribute to have explicit ForeignKey relation fields

https://github.com/django/django/commit/24ec9538b7ca400f68ba08fab380445ca95d7c02 introduced an opportunity to order by the ForeignKey field attr itself.
But check method didn't reflect this change so it was fixed by this patch. Also 2 tests were added for new check method behaviour.
Plus fixed a small typo in method comment.