Bump workflow versions

[MaximilianAlgehed]

Trying to bring things up to date to make sure the issues we've seen in CI on #397 aren't due to old versions.

[MaximilianAlgehed]

@nick8325 here is something we need to discuss. The old ci system has stopped working due to random github actions deprecations. I've updated to the latest version of haskell-ci and bumped the ci script. However, a consequence of this is that we can no longer support ghc versions older than 8.0.2 in ci.

Should we make the decision to discontinue ghc 7 support?

[MaximilianAlgehed]

@UlfNorell thoughts on this?

[MaximilianAlgehed]

Current state of things here:

1. We can support 7.10.3 since that's supported by setup-haskell
2. We change to setup-haskell as that gives us more flexibility than depending on haskell-ci
3. I've set up the workflow to run as a cronjob nightly so that we see CI breaking earlier than in a PR (which is what happened here)

[UlfNorell]

If nothing else this greatly simplifies the CI setup. It seems to me the question here isn't should we drop ghc-7 support, but rather getting CI to run at all. If we want to keep support for older versions that's something that can be figured out later.