armadillo: 8.400.0 -> 8.500.0

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

This update was made based on information from https://repology.org/metapackage/armadillo/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 8.500.0 with grep in /nix/store/4b5v6xvxsbdqgwlqnj421wa0cwhdpw4p-armadillo-8.500.0
- directory tree listing: https://gist.github.com/5849376cdd72ab243c8f004589cb24ec