/usr/lib/ruby/ is in ruby-rack-accept 0.4.5-3.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/rack/
/usr/lib/ruby/vendor_ruby/rack/accept/
/usr/lib/ruby/vendor_ruby/rack/accept/request.rb
/usr/lib/ruby/vendor_ruby/rack/accept/charset.rb
/usr/lib/ruby/vendor_ruby/rack/accept/media_type.rb
/usr/lib/ruby/vendor_ruby/rack/accept/encoding.rb
/usr/lib/ruby/vendor_ruby/rack/accept/header.rb
/usr/lib/ruby/vendor_ruby/rack/accept/language.rb
/usr/lib/ruby/vendor_ruby/rack/accept/context.rb
/usr/lib/ruby/vendor_ruby/rack/accept/response.rb
/usr/lib/ruby/vendor_ruby/rack/accept/version.rb
/usr/lib/ruby/vendor_ruby/rack/accept.rb