ptex: 2.1.28 -> 2.1.33

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

This update was made based on information from https://repology.org/metapackage/ptex/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.)
- directory tree listing: https://gist.github.com/88ea582c17048ee1efddf1b2e87ef3bc