bump Nokogiri version to v1.18.9 to resolve GHSA-353f-x4gh-cqq8

nokogiri in the newest version of 1.18.9 (9.0.4 ships 1.18.8) fixes several HIGH and CRITICAL Vulnerabilities summarized in [GHSA-353f-x4gh-cqq8](https://github.com/advisories/GHSA-353f-x4gh-cqq8). Could you please check to include it in the next regular release? Thanks!