CI: drop validation of GHC 7

Changes:
- bump GHC_FOR_RELEASE to 9.4.8
- bump action versions
- uniform quoting style
- satisfy actionlint
- fix order: setup Haskell before cache restore (uses setup.haskell-outputs)
- use `--ignore-project` in `cabal install hackage-repo-tool`
- use GHC_FOR_RELEASE also in validate-old-ghcs
- closes haskell#8858: deleted comment
- closes haskell#9858 by dropping container and using ghcup to setup ghcs

GHCs that do not install on ubuntu-22.04 with GHCup are dropped, meaning we only keep GHC 8.0.2 and up.