fix(ci): install Chromium before running Lighthouse CI

lhci autorun requires Chrome to be present on the runner. This was
causing the lighthouse job to fail with "Chrome installation not found".

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -57,6 +57,8 @@ jobs:
           cache: npm
       - run: npm ci
       - run: npm run build
+      - name: Install Chromium
+        uses: browser-actions/chromium@v3
       - name: Run Lighthouse CI
         run: |
           npm install -g @lhci/cli