/usr/lib/ruby/vendor_ruby/ is in larch 1.1.2-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/larch/
/usr/lib/ruby/vendor_ruby/larch/config.rb
/usr/lib/ruby/vendor_ruby/larch/db/
/usr/lib/ruby/vendor_ruby/larch/db/account.rb
/usr/lib/ruby/vendor_ruby/larch/db/mailbox.rb
/usr/lib/ruby/vendor_ruby/larch/db/message.rb
/usr/lib/ruby/vendor_ruby/larch/db/migrate/
/usr/lib/ruby/vendor_ruby/larch/db/migrate/001_create_schema.rb
/usr/lib/ruby/vendor_ruby/larch/db/migrate/002_add_timestamps.rb
/usr/lib/ruby/vendor_ruby/larch/errors.rb
/usr/lib/ruby/vendor_ruby/larch/imap/
/usr/lib/ruby/vendor_ruby/larch/imap/mailbox.rb
/usr/lib/ruby/vendor_ruby/larch/imap.rb
/usr/lib/ruby/vendor_ruby/larch/logger.rb
/usr/lib/ruby/vendor_ruby/larch/monkeypatch/
/usr/lib/ruby/vendor_ruby/larch/monkeypatch/net/
/usr/lib/ruby/vendor_ruby/larch/monkeypatch/net/imap.rb
/usr/lib/ruby/vendor_ruby/larch/version.rb
/usr/lib/ruby/vendor_ruby/larch.rb