xscreensaver: 5.38 -> 5.39

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

This update was made based on information from https://repology.org/metapackage/xscreensaver/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 5.39 with grep in /nix/store/gbzmzb9nq2frp4q1mmz2946gzcx536v3-xscreensaver-5.39
- directory tree listing: https://gist.github.com/aa36e0385c0160a833c83693ce83be28