Fix CI Nix materialization check on release (#3180)

Author: goodlyrottenapple

.github/workflows/release.yml

@@ -13,13 +13,12 @@ jobs:
         with:
           submodules: recursive
 
-      - name: Install Nix
-        uses: cachix/install-nix-action@v14.1
+      - name: 'Install Nix'
+        uses: cachix/install-nix-action@v15
         with:
           extra_nix_config: |
-            substituters = http://cache.nixos.org https://hydra.iohk.io
+            substituters = http://cache.nixos.org https://cache.iog.io
             trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
-          install_url: "https://releases.nixos.org/nix/nix-2.3.16/install"
 
       - name: Install Cachix
         uses: cachix/cachix-action@v10
@@ -28,8 +27,19 @@ jobs:
           extraPullNames: 'kore'
           skipPush: true
 
+      - name: Materialize
+        run: nix run .#update-cabal
+
+      - name: Materialize GHC 9
+        run: nix run .#update-cabal-ghc9
+
       - name: Check materialization
-        run: nix-build --arg checkMaterialization true -A project.stack-nix
+        run: |
+          if [ -n "$(git status --porcelain 'nix/')" ]; then
+            echo 2>&1 "Error: found modified files"
+            git diff
+            exit 1
+          fi
 
   release:
     name: 'Release'

.github/workflows/update.yml

@@ -43,10 +43,10 @@ jobs:
 
 
       - name: Materialize
-        run: GC_DONT_GC=1 nix run .#update-cabal
+        run: nix run .#update-cabal
 
       - name: Materialize GHC 9
-        run: GC_DONT_GC=1 nix run .#update-cabal-ghc9
+        run: nix run .#update-cabal-ghc9
 
       - name: Update branch
         env: