adapta-gtk-theme: 3.93.1.16 -> 3.93.1.18 (#41124)

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

This update was made based on information from https://repology.org/metapackage/adapta-gtk-theme/versions.

These checks were done:

- built on NixOS

- 0 of 0 passed binary check by having a zero exit code.
- 0 of 0 passed binary check by having the new version present in output.
- directory tree listing: https://gist.github.com/60eadc1cf0cabf6d0def6a21d1d21c5d
- du listing: https://gist.github.com/afad29a6d76aa88ae6df876a0d28f599