`repNonArrowKind` was missing a case for `HsKindSig`, which this
commit adds. Fixes #13781.

Test Plan: make test TEST=T13781

Reviewers: goldfire, austin, bgamari

Reviewed By: goldfire

Subscribers: rwbarton, thomie

GHC Trac Issues: #13781

Differential Revision: https://phabricator.haskell.org/D3627