Prevent README.md and CODE-OF-CONDUCT.md to trigger CI

[angerman]

Maybe the better option is:

paths:
  # trigger if the workflow changed
  - ".github/workflows/**"
  # trigger if the flake changed
  - "flake.*"
  # trigger if nix, scripts, or _sources changed
  - "nix/**"
  - "scripts/**"
  - "_sources/**"

The rational here is that PRs that don't change nay of those, should not take 10-20min CI run for what is actually wasted compute. There are no changes that influence the output of the runs.

[michaelpj]

This can't work, unfortunately: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/troubleshooting-required-status-checks#handling-skipped-but-required-checks

I've seen other projects use https://github.com/fkirc/skip-duplicate-actions to get around this.

I'd also just like to try and speed up the checks. The nix checks should be all cache hits in such a situation, the bottlenecks are building the repo (which also should be pretty fast), Nix evaluation, ( :( ) and uploading and downloading it as an artifact. Seee https://github.com/input-output-hk/cardano-haskell-packages/issues/165 and https://github.com/input-output-hk/cardano-haskell-packages/issues/171. Ideas welcome!