Make some absltest type comments compatible with upcoming pytype release.
Make some absltest type comments compatible with upcoming pytype release.

For variables, Pytype will begin checking the declared types against the
assigned types, so type comment "casts" need adjustment to pass type checking.

PiperOrigin-RevId: 311595738
Change-Id: I0ae22b4cd25568adfc4a3ed4de2faf88395c45c9

abseil/abseil-py,abseil/abseil-py