as a user I would like to see my unapproved PRs sorted to the top of "Pull requests to review" list

If I have many open PRs to review, some may be hidden behind a "Show XX more" link.
This obscures PRs that I may not have got around to reviewing.
Since the point of the overview page appears to be "Your Work" it makes sense to display as prominently as possible work that still needs to be done.