Getting rid of out-of-band attributes in haskell/security-advisories

[MangoIV]

there's a lot of issues that depend on this:

• Nix integration #36 because nix filters out git dirs
• CI integration #27
• add actual tests #19

It also adds the dependency on git and relies on peculiarities of its implementation (see e.g. the UTCTime vs ZonedTime issue.

[blackheaven]

hsec-sync will avoid this problem.

[MangoIV]

Neat. I’ll have a look!