CI: add nix

Author: nim65s

.github/workflows/nix.yml

@@ -0,0 +1,39 @@
+name: "CI - Nix"
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  nix:
+    runs-on: "${{ matrix.os }}-latest"
+    strategy:
+      matrix:
+        os: [ubuntu, macos]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v31
+      - uses: cachix/cachix-action@v16
+        with:
+          name: gepetto
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - run: nix build -L
+
+  check:
+    if: always()
+    name: check-macos-linux-nix
+
+    needs:
+      - nix
+
+    runs-on: Ubuntu-latest
+
+    steps:
+      - name: Decide whether the needed jobs succeeded or failed
+        uses: re-actors/alls-green@release/v1
+        with:
+          jobs: ${{ toJSON(needs) }}