Fix CI #2

ci/default.nix

@@ -17,8 +17,11 @@ let
 
   cabalSrc = sources.mpickering-cabal.outPath;
 
+  haskellPackagesWithCabal = haskellPackages.extend (self: super:
+        cabalDependenciesOverrides self
+  );
+
   haskellPackages = haskellPackages_.extend (self: super:
-        cabalDependenciesOverrides self //
         {
         semaphore-compat = self.callHackage "semaphore-compat" "1.0.0" {};
         cabal-plan = self.callHackage "cabal-plan" "0.7.3.0" {};
@@ -94,7 +97,7 @@ let
     let
       deps = [
         bash curl gnutar findutils patch rsync openssl
-        haskellPackages.cabal-install haskellPackages.ghc gcc binutils-unwrapped pwgen gnused
+        haskellPackagesWithCabal.cabal-install haskellPackages.ghc gcc binutils-unwrapped pwgen gnused
         hackage-repo-tool overlay-tool python3 jq pkg-config
         git # cabal-install wants this to fetch source-repository-packages
         postgresql libmysqlclient.dev