ci: add cachix workflow (#740)

.github/workflows/cachix.yml

@@ -0,0 +1,29 @@
+# Publish the Nix flake outputs to Cachix
+name: Cachix
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  publish:
+    name: Publish Flake
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@v4
+
+    - name: Install nix
+      uses: cachix/install-nix-action@v25
+
+    - name: Authenticate with Cachix
+      uses: cachix/cachix-action@v14
+      with:
+        name: yazi
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
+    - name: Build nix flake
+      run: nix build -L