pytest-forked removed support for python2 in their 1.4.0 release,
breaking the pinned version of mutagen that the old version of
spotify-ripper requires. We rebase onto another fork that has updated it
a bit, adding support for python3 and unpinning their dependencies.
Required as part of the latest staging-next commit set to Nixpkgs [1].
Note that this breaks builds on all current non-unstable Nixpkgs
branches (but as the repository notes, they are not supported anyway).
[1]: 02924cf951/doc/languages-frameworks/qt.section.md
