add ipv6 checks

.github/workflows/test-only.yml

@@ -68,6 +68,9 @@ jobs:
           # Should return 0 (no error) when grep finds it
           curl -s http://localhost:5556 |grep -q checkbox-uuid
           curl -s http://localhost:5556/rss|grep -q rss-specification
+          # and IPv6
+          curl -s http://[::]:5556|grep -q checkbox-uuid
+          curl -s http://[::]:5556/rss|grep -q rss-specification
 
 #export WEBDRIVER_URL=http://localhost:4444/wd/hub
 #pytest tests/fetchers/test_content.py