/usr/lib/ruby/vendor_ruby/concurrent/synchronization/ is in ruby-concurrent 1.0.0-3.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/abstract_lockable_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/abstract_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/abstract_struct.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/condition.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/jruby_lockable_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/jruby_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/lock.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/lockable_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/mri_lockable_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/mri_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/rbx_lockable_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/rbx_object.rb
/usr/lib/ruby/vendor_ruby/concurrent/synchronization/volatile.rb