.github: run on ubuntu-24.04

[wolfgangwalther]

The ubuntu-20.04 runners have been deprecated and disabled.

Side note: A bit annoying, that haskell-ci is so outdated on hackage and thus in nixpkgs. The dev shell for cabal2nix provides it, but it's way too old, so I had to build it from source. Tried updating it in nixpkgs to an unstable version, but didn't succeed, yet.

[wolfgangwalther]

We have some warnings, but an error inbetween as well:

 Error: [git-protocol] Cloning over git:// might lead to an arbitrary code
execution vulnerability. Furthermore, popular forges like GitHub do not
support it. Use https:// or ssh:// instead.

I assume this is about:

source-repository head
  type:     git
  location: git://github.com/NixOS/cabal2nix.git
  subdir:   hackage-db

in hackage-db/hackage-db.cabal.

[sternenseemann]

I used to maintain a haskell-ci-unstable attribute, then they released frequently for a bit, but not anymore (for quite a while). Maybe I should bring it back. Unfortunately, the whole package is a massive pain, but I'm not sure about alternatives for a nixpkgs independent CI for Haskell (which is quite useful for cabal2nix).

[sternenseemann]

What do you think? Should we maintain an unstable haskell-ci again?

[wolfgangwalther]

Even if we do, we'd still be playing ping-pong between here and nixpkgs, at least assuming we'd somehow want to pin the version used in this repo. Which I think we really need to do, otherwise everyone on a stable channel will not be able to run it.

How about we maintain the unstable haskell-ci as an override in this repo's shell.nix? That would make it reproducible to run, too.