CI: caching is likely broken

[andreasabel]

CI caches are likely stale (most are from 2023):

A more flexible cache key is needed, either involving github.sha or a hash of the build plan in dist-newstyle/cache/plan.json (create with cabal build ... --dry-run).

Also due to XDG it could be that the wrong directory is cached now (but this would not matter since the restored caches are anyway hopelessly outdated):

unix/.github/workflows/ci.yml

Lines 41 to 45 in a64ce6d

	- uses: actions/cache@v4
	name: Cache cabal stuff
	with:
	path: |
	~/.cabal/store