Add workflow to build and test

.gitea/workflows/build.yaml

@@ -0,0 +1,22 @@
+name: Build & Test
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  nix-build:
+    runs-on: nix
+    steps:
+      - uses: actions/checkout@v3
+      - name: Run checks
+        run: nix flake check
+      - name: Build
+        run: nix build
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v3
+        with:
+          path: result
+          name: build