Upgrade the pytype version to one that can parse the tkinter stubs. (#4456)

The latest pytype release fixes two pyi parser bugs that allow files
affected by them to be taken off the pytype exclude list. I removed two
`total=False` declarations in tkinter/__init__ that pytype does not like
(because it checks that `total` is present only when TypedDict is a
class's immediate parent) and which shouldn't be needed because
_InMiscNonTotal already specifies totality. I double-checked that mypy
reports no errors in 3.7 on a .py file containing:

  from typing_extensions import TypedDict
  Foo = TypedDict('Foo', {'x': int}, total=False)
  class Bar(Foo): pass
  x: Foo = {}

showing that it doesn't require `total` to be repeated.

requirements-tests-py3.txt

@@ -5,4 +5,4 @@ flake8==3.8.3
 flake8-bugbear==20.1.4
 flake8-pyi==20.5.0
 isort[pyproject]==5.1.1
-pytype>=2020.07.30
+pytype>=2020.08.17