There was a lot of copy-pasta code between the finder and pr status. After
some investigation it was clear that the prSelectorForCurrentBranch code
was really just a duplicate of the finder's code without actually making
the API call for the PR. Since the ParsePRRefs helper had already
extracted much of the logic for determining a PR's head ref branch, I was
able to reuse it in gh pr status with a small refactor.