Switch GHCup to vanilla channel

Author: fendor

.github/scripts/common.sh

@@ -137,6 +137,9 @@ install_ghcup() {
 	else
 		curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | BOOTSTRAP_HASKELL_MINIMAL=1 sh
 		source "$(dirname "${GHCUP_BIN}")/env"
+		# make sure we use the vanilla channel for installing binaries
+		# see https://github.com/haskell/ghcup-metadata/pull/166#issuecomment-1893075575 
+		ghcup config set url-source https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-vanilla-0.0.8.yaml
 		ghcup install cabal --set "${BOOTSTRAP_HASKELL_CABAL_VERSION}"
 	fi
 }