Problem: CI is triggered only on push, so it won't work in case of
PRs from forks.
Solution: trigger it on PRs as well. Trigger on push only when the
branch is master.
If you want to run on push to your feature branch, you can edit
check.yml in your branch.
Problem: node16 is now deprecated and github-runner provided by nixpkgs
no longer supports this runtime. However, "actions/checkout@v3" uses
this runtime.
Solution: Update CI pipeline to use "actions/checkout@v4".
Problem: We have introduced a new template for Haskell libraries and
need to update this package according to this template.
Solution: Use new template, bump dependencies, remove unused license,
apply formatting and hlint suggestions.
