ci: improve CI speed by utilizing caching

Signed-off-by: Christina Sørensen <[email protected]>

.github/workflows/build.yml

@@ -4,8 +4,10 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
-    - uses: cachix/install-nix-action@v27
-      with:
-        nix_path: nixpkgs=channel:nixos-24.05
-    - run: nix --experimental-features "nix-command flakes" flake check
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - name: Setup Nix cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+      - run: nix --experimental-features "nix-command flakes" flake check