CI: nix build and push to cachix

.forgejo/workflows/ci.yaml

@@ -0,0 +1,18 @@
+on: push
+
+env:
+  CACHIX_NAME: git-fnordig
+
+jobs:
+  Publish:
+    runs-on: flakes-action
+    steps:
+      - uses: actions/checkout@v3
+        name: Checkout
+      - name: Set up Cachix
+        run: |
+            nix-env -iA nixpkgs.cachix nixpkgs.bash
+            cachix use $CACHIX_NAME
+      - name: Build
+        run: |
+          cachix watch-exec $CACHIX_NAME nix build