Add nekohtml advisory based on nokogiri advisory

[jasnow]

Add nekohtml advisory based on nokogiri advisory

• gems/nekohtml/CVE-2022-24839.yml

[flavorjones]

I personally don't think it's necessary to create this file.

1. The Nokogiri fork of nekohtml is not available as a ruby gem.
2. It is ONLY vendored in Nokogiri, and gems/nokogiri/CVE-2022-24839.yml already exists to notify people to upgrade Nokogiri.

So I don't know who's going to use this information, or how it will be actionable.

I recommend closing without merging, but will defer to the other maintainers if they feel strongly it should be part of the record.

[jasnow]

Based on @flavorjones and @simi feedback, I will closing this PR.