added nix build to CI

.github/workflows/nix.yaml

@@ -16,6 +16,21 @@ jobs:
     - uses: cachix/cachix-action@v15
       with:
         name: nexus-ci
-        # If you chose API tokens for write access OR if you have a private cache
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     - run: nix develop -c nixpkgs-fmt --check .
+
+  build:
+    name: Build NixOS config
+    runs-on: ubuntu-24.04
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v30
+    - uses: cachix/cachix-action@v15
+      with:
+        name: nexus-ci
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - name: Build NixOS machines
+      run: |
+        nix build .#nixosConfigurations.servers-us-east-1.config.formats.linode
+    - name: Run Flake Checks
+      run: nix flake check