installing nix in the github action

.github/workflows/build.yml

@@ -19,12 +19,9 @@ jobs:
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
-
-      # Checks-out the repository under $GITHUB_WORKSPACE, so your job can access it
-      - name: Checkout repo
-        uses: actions/checkout@v2
-
-      # Runs the flake
-      - name: Build
-        run: |
-          nix build
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v25
+      with:
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+    - run: nix build
+    - run: nix flake check