Rails 7.2 compatible Rubies

1. Add Ruby 2.7 specific Gemfile that uses an older version of nokogiri
2. Rails edge doesn't support Ruby 2.7.0, so exclude it.
3. Add Ruby 3.3
4. Update Gemfile.lock to test against Rails 7.1.2 as it's the latest
   version.
5. Remove continue-on-error from the matrix and always set to true

gemfiles/ruby_2.7.gemfile

@@ -0,0 +1,6 @@
+source 'https://rubygems.org'
+git_source(:github) { |repo| "https://github.com/#{repo}.git" }
+
+gemspec path: "../"
+
+gem "nokogiri", "~> 1.15.0"