Update GitHub Pages nokogiri >= 1.12.5

[AutomationPanda]

The repository has a security vulnerability: https://github.com/q2ebanking/boa-constrictor/security/dependabot/docs/Gemfile.lock/nokogiri/open

Unfortunately, GitHub Pages current supports nokogiri = 1.11.7: https://pages.github.com/versions/

I opened a GitHub Support ticket to get this updated: https://support.github.com/ticket/personal/0/1332394

Once the support ticket is resolved, we should update Boa Constrictor.