Use six.add_metaclass instead of six.with_metaclass in parameterized.TestCase
Use six.add_metaclass instead of six.with_metaclass in parameterized.TestCase

This allows static analysis tools to infer the base classes without any
six-specific special-casing.

PiperOrigin-RevId: 317822776
Change-Id: I94c5b5785732ad42e00ebe17f5fc8292ba5c0a0a

abseil/abseil-py,abseil/abseil-py