/usr/lib/ruby/vendor_ruby/ is in ruby-memfs 0.5.0-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/memfs/
/usr/lib/ruby/vendor_ruby/memfs.rb
/usr/lib/ruby/vendor_ruby/memfs/dir.rb
/usr/lib/ruby/vendor_ruby/memfs/fake/
/usr/lib/ruby/vendor_ruby/memfs/fake/directory.rb
/usr/lib/ruby/vendor_ruby/memfs/fake/entry.rb
/usr/lib/ruby/vendor_ruby/memfs/fake/file/
/usr/lib/ruby/vendor_ruby/memfs/fake/file.rb
/usr/lib/ruby/vendor_ruby/memfs/fake/file/content.rb
/usr/lib/ruby/vendor_ruby/memfs/fake/symlink.rb
/usr/lib/ruby/vendor_ruby/memfs/file/
/usr/lib/ruby/vendor_ruby/memfs/file.rb
/usr/lib/ruby/vendor_ruby/memfs/file/stat.rb
/usr/lib/ruby/vendor_ruby/memfs/file_system.rb
/usr/lib/ruby/vendor_ruby/memfs/filesystem_access.rb
/usr/lib/ruby/vendor_ruby/memfs/io.rb
/usr/lib/ruby/vendor_ruby/memfs/version.rb