Test the build setup on Windows in CI too

We don't deploy on Windows, but this is useful to ensure the development
setup works correctly for contributors (it was broken recently). We
don't bother with the integration tests, since contributors won't
usually need these and they're a bit more complicated (requires
launching & managing the server backend).

Author: pimterry

.github/workflows/ci.yml

@@ -48,11 +48,38 @@ jobs:
           path: dist/*
           if-no-files-found: error
 
+  # We build in parallel on Windows too, purely to check the build process is cross-compatible for contributors.
+  test-windows-build:
+    name: Test build on Windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 100
+
+      # Install Node
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20.8.0
+          cache: 'npm'
+
+      # Install & unit test & build
+      - run: npm ci
+
+      - run: npm run test:unit
+
+      # Build the app:
+      - name: Test a production build
+        run: npm run build
+        if: github.ref != 'refs/heads/main'
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # To pull server without rate limit issues in CI
+
   publish-netlify:
     name: Deploy ${{ (github.ref == 'refs/heads/main' && 'to Netlify production') || 'Netlify preview' }}
     if: github.event_name == 'push'
     runs-on: ubuntu-latest
-    needs: build
+    needs: [build, test-windows-build]
     steps:
       - uses: actions/checkout@v4