Revert "Try to use the preinstalled ghcup GHCs on GHA, again"
Revert "Try to use the preinstalled ghcup GHCs on GHA, again"

This reverts commit 200c9e5dd20d566803bd115e5013e6ce14f0aab7.

Let me leave the arcane art of tweaking of haskell-ci to my betters.

LambdaHack/LambdaHack