fix: build the playground before starting the cypress tests

.github/workflows/tests.yml

@@ -60,6 +60,7 @@ jobs:
       - name: Run end-to-end tests
         uses: cypress-io/github-action@v6
         with:
+          build: yarn playground:build
           start: yarn playground:start
       - uses: actions/upload-artifact@v4
         if: failure()