/usr/lib/ruby/ is in ruby-directory-watcher 1.5.1-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/directory_watcher/
/usr/lib/ruby/vendor_ruby/directory_watcher.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/collector.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/configuration.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/coolio_scanner.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/em_scanner.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/event.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/eventable_scanner.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/file_stat.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/logable.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/notifier.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/paths.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/rev_scanner.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/scan.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/scan_and_queue.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/scanner.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/threaded.rb
/usr/lib/ruby/vendor_ruby/directory_watcher/version.rb