DEV: Update nokogiri to 1.18.1 (#30554)

Nokogiri/libxml is now more strict in terms of params it receives.

It uses kwargs vs options object (I fixed an issue there in #30545) doesn't accept nil/blank html (fixed here) and most importantly handles encoding in a different way. It seems to require explicitly specifying UTF8.

* Build(deps): Bump nokogiri from 1.16.8 to 1.18.1

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.16.8 to 1.18.1.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.16.8...v1.18.1)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

script/import_scripts/disqus.rb

@@ -17,7 +17,7 @@ class ImportScripts::Disqus < ImportScripts::Base
     abort("Category #{IMPORT_CATEGORY} not found") if @category.blank?
 
     @parser = DisqusSAX.new
-    doc = Nokogiri::XML::SAX::Parser.new(@parser)
+    doc = Nokogiri::XML::SAX::Parser.new(@parser, Encoding::UTF_8)
     doc.parse_file(IMPORT_FILE)
     @parser.normalize