Drop old MacOS jobs

[Bodigrim]

Drop old MacOS jobs: there are no bindists of old GHCs for aarch64, which macos-latest now refers to.

We could potentially stick to macos-13 instead, but whatever, I don't really care that much about old GHCs.

[Bodigrim]

Oh well, there is no preinstalled ghcup on macos-latest runners. Shall we use haskell-actions/setup?

[hasufell]

I'm not a fan of the action. We can just do:

curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | BOOTSTRAP_HASKELL_NONINTERACTIVE=1 BOOTSTRAP_HASKELL_INSTALL_NO_STACK=1 BOOTSTRAP_HASKELL_GHC_VERSION=${{ matrix.ghc }} BOOTSTRAP_HASKELL_ADJUST_BASHRC=yes sh
. ~/.ghcup/env
# install/build