Bumping Nixpkgs Haskell infrastructure to LTS-21, GHC-9.4

The Haskell maintainers in Nixpkgs are currently in the process of bumping the main Haskell package set to GHC-9.4, LTS-21.

There are many Haskell packages no longer compiling after this bump, and we’d love to get help fixing things from people using the Haskell package set in Nixpkgs.

You can find more information on the NixOS Discourse: