added nix fmt to CI

.github/workflows/ci.yaml

@@ -45,6 +45,13 @@ jobs:
     with:
       cargo-profile: ${{ needs.check-inputs.outputs.cargo-profile }}
 
+  nix:
+    name: Nix
+    needs: check-inputs
+    uses: ./.github/workflows/nix.yaml
+    with:
+      deploy: ${{ needs.check-inputs.outputs.is-default-branch == 'true' }}
+
   container:
     name: Container
     needs: [rust, check-inputs]

.github/workflows/nix.yaml

@@ -0,0 +1,21 @@
+name: Nix CI
+on:
+  workflow_call:
+    inputs:
+      deploy:
+        required: true
+        type: boolean
+
+jobs:
+  fmt:
+    name: Check Nix Formatting
+    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
+        # 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 .