Motivation for this change

3.1 was released upstream which fixes* natumbri/mopidy-youtube#150.

* Added asterisk because GitHub otherwise marks this pull request as fixing that bug due to the magic fixes word.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Tested by building

buildEnv {
  name = "mopidy-with-extensions-${mopidy.version}";
  paths = lib.closePropagation [
    pkgs.mopidy-iris
    pkgs.mopidy-local
    pkgs.mopidy-youtube
  ];
  pathsToLink = [ "/${mopidyPackages.python.sitePackages}" ];
  buildInputs = [ makeWrapper ];
  postBuild = ''
    makeWrapper ${mopidy}/bin/mopidy $out/bin/mopidy \
      --prefix PYTHONPATH : $out/${mopidyPackages.python.sitePackages}
  '';
}

The upstream bug affected me, and I can confirm that this update resolved it.