knot-dns: 2.6.5 -> 2.6.6

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

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

These checks were done:

- built on NixOS
- ran ‘/nix/store/p1k7d2y5aa4haxlkkn2jadviwvl5plcc-ipset-6.38/bin/ipset -h’ got 0 exit code
- ran ‘/nix/store/p1k7d2y5aa4haxlkkn2jadviwvl5plcc-ipset-6.38/bin/ipset --help’ got 0 exit code
- ran ‘/nix/store/p1k7d2y5aa4haxlkkn2jadviwvl5plcc-ipset-6.38/bin/ipset help’ got 0 exit code
- found 2.6.6 in filename of file in /nix/store/p1k7d2y5aa4haxlkkn2jadviwvl5plcc-ipset-6.38
- directory tree listing: https://gist.github.com/f62ed14efd30650e1e05f1af8d5c2af4