gh-100098: [Enum] insist on actual tuples, no subclasses, for auto (GH-100099)

When checking for auto() instances, only top-level usage is supported,
which means either alone or as part of a regular tuple. Other
containers, such as lists, dicts, or namedtuples, will not have auto()
transformed into a value.
(cherry picked from commit ded02ca54d7bfa32c8eab0871d56e4547cd356eb)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>