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

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

These checks were done:

- built on NixOS
- Warning: no invocation of /nix/store/7mjpw971bh37wil41hin4ssn290wr3ad-ngspice-28/bin/cmpp had a zero exit code or showed the expected version
- /nix/store/7mjpw971bh37wil41hin4ssn290wr3ad-ngspice-28/bin/ngspice passed the binary check.
- 1 of 2 passed binary check by having a zero exit code.
- 0 of 2 passed binary check by having the new version present in output.
- found 28 with grep in /nix/store/7mjpw971bh37wil41hin4ssn290wr3ad-ngspice-28
- directory tree listing: https://gist.github.com/890c9d6d1b1aa9e86b2f4c8ddf86a36d
- du listing: https://gist.github.com/099b236d47fee839749355d18a841493

ngspice: 27 -> 28