update for mypy 1.0 dev

update for mypy 1.0 dev

As I need dmypy to work without facing [1], I am
running the latest build of mypy which seems so far
to finally not have that issue.

update constructs that latest mypy is being more picky
about, including better typing for the _NONE_NAME
symbol used in constraints (porting those elements
from the Enum patch at
I15ac3daee770408b5795746f47c1bbd931b7d26d)

[1] https://github.com/python/mypy/issues/12744

Change-Id: Ib3f56787fa65ea9bb2e6a0bccc4d99f54c516dad