mate.mate-themes: 3.22.15 -> 3.22.16

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/mate-themes/versions.

These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 3.22.16 with grep in /nix/store/vjm6m5yyzsrwv51iryqq326w3829dx2c-mate-themes-3.22.16
- directory tree listing: https://gist.github.com/d3a254df8c888718ac16edea0d4dce1d