Silence upcoming type errors in Python 3.9.
Silence upcoming type errors in Python 3.9.

PiperOrigin-RevId: 433748978
Change-Id: Ic18ef76d5a6453231f4eab0af5ffb953b6f1a7ee
GitOrigin-RevId: 4067fb2015de3b32c28e6ce8b0004cd7e7e2709a

deepmind/xmanager,deepmind/xmanager