nixpkgs currently mixes sgtpuzzles/sgt-puzzles across filenames,
packages, tests.
This inconsistency is frequently annoying.
Let's unify on "sgt-puzzles", on the basis that:
* "sgt-puzzles" is the package filename.
* Alpine/FreeBSD/Debian use "sgt-puzzles". No other distro uses
"sgtpuzzles". https://repology.org/project/sgt-puzzles/versions
