Apply suggestion by @smelc

Co-authored-by: Clément Hurlin <smelc@users.noreply.github.com>

.github/workflows/hls.yml

@@ -12,8 +12,17 @@ jobs:
   test-hls-works:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c
-    - uses: cachix/install-nix-action@daddc62a2e67d1decb56e028c9fa68344b9b7c2a
-      with:
-        nix_path: nixpkgs=channel:nixos-23.11
-    - run: nix develop --accept-flake-config --command bash -c "cabal update; haskell-language-server"
+      - uses: actions/checkout@v4
+      - name: Install Nix with good defaults
+        uses: input-output-hk/install-nix-action@v20
+        with:
+          extra_nix_config: |
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = https://cache.iog.io/ https://cache.nixos.org/
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/install-nix-action@v18
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      # Make the Nix environment available to next steps
+      - uses: rrbutani/use-nix-shell-action@v1
+      - run: cabal update && haskell-language-server