fvwm: 2.6.7 -> 2.6.8 (#41565)

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

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

These checks were done:

- built on NixOS
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm2 passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-perllib passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-convert-2.6 passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-menu-xlock passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-menu-directory passed the binary check.
- Warning: no invocation of /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-menu-desktop had a zero exit code or showed the expected version
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-menu-headlines passed the binary check.
- Warning: no invocation of /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/xpmroot had a zero exit code or showed the expected version
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/FvwmCommand passed the binary check.
- Warning: no invocation of /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-root had a zero exit code or showed the expected version
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-config passed the binary check.
- /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8/bin/fvwm-bug passed the binary check.
- 10 of 13 passed binary check by having a zero exit code.
- 3 of 13 passed binary check by having the new version present in output.
- found 2.6.8 with grep in /nix/store/kycw0a7gqxh0v7lxq001j9sjysnz1v6h-fvwm-2.6.8
- directory tree listing: https://gist.github.com/94e21d8ab3a4808980c94f1fbb20f1b6
- du listing: https://gist.github.com/6db3d3e079f7808b93a1bbc20e5f396e