fix broken Qt 4.8 Linux build after wkhtmltopdf/packaging#86

.github/workflows/official.yml

@@ -20,6 +20,10 @@ jobs:
         with:
           repository: wkhtmltopdf/packaging
           path: packaging
+      - name: configure docker
+        run:  |
+          echo '{ "experimental": true }' | sudo tee /etc/docker/daemon.json
+          sudo systemctl restart docker
       - name: build
         run: cd packaging && python3 ./build package-docker buster-amd64 ../wkhtmltopdf