Bug: doesn't check rubygems anymore

[adamzapasnik]

The file structure of https://github.com/rubysec/ruby-advisory-db has changed. libraries dir was removed and its files moved to gems/rubygems-update dir. Therefore existing code doesn't work with the new file structure.

Probably there should be a scheduled Github action that runs tests every week against https://github.com/rubysec/ruby-advisory-db 🤔