Re-add a test workflow for pull requests

.github/workflows/test.yaml

@@ -0,0 +1,27 @@
+---
+name: Test and Build
+
+on:
+  pull_request:
+
+jobs:
+  test_and_build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: cachix/install-nix-action@v26
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      - uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: ./run ci:install
+
+      - name: Run tests
+        run: ./run ci:test
+
+      - name: Generate the website
+        run: |
+          ./run ci:build
+          tree output_prod