Don't install stack install hook

See https://github.com/commercialhaskell/stack/issues/5895

Stack feature is documented here:
  https://docs.haskellstack.org/en/stable/yaml_configuration/#ghc-installation-customisation

It's recommended, but probably too unexpected for CI.
It means stack will not install GHC on its own, but through GHCup.

images/linux/scripts/tests/Haskell.Tests.ps1

@@ -31,4 +31,8 @@ Describe "Haskell" {
     It "Stack" {
         "stack --version" | Should -ReturnZeroExitCode
     }
+
+    It "Stack hook is not installed" {
+        "$HOME/.stack/hooks/ghc-install.sh" | Should -Not -Exist
+    }
 }