bpo-44929: [Enum] Fix global repr (GH-27789)

* Fix typo in __repr__ code

* Add more tests for global int flag reprs

* use last module if multi-module string
  - when an enum's `__module__` contains several module names, only
     use the last one

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Ethan Furman <ethan@stoneleaf.us>