nsd: 4.1.20 -> 4.1.21

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

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

These checks were done:

- built on NixOS
- /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21/bin/nsd passed the binary check.
- Warning: no invocation of /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21/bin/nsd-checkconf had a zero exit code or showed the expected version
- /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21/bin/nsd-checkzone passed the binary check.
- Warning: no invocation of /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21/bin/nsd-control had a zero exit code or showed the expected version
- Warning: no invocation of /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21/bin/nsd-control-setup had a zero exit code or showed the expected version
- 2 of 5 passed binary check by having a zero exit code.
- 0 of 5 passed binary check by having the new version present in output.
- found 4.1.21 with grep in /nix/store/vwidqdayh0l8rf5sjq37hr6ygdxrmkbb-nsd-4.1.21
- directory tree listing: https://gist.github.com/57f572db82ca8e038bcf1c970d13f10e
- du listing: https://gist.github.com/11c687e733f7222872d6e3733c5f9d0b