Update python-mypy to 0.770

Summary:
Full changelog here

Depends on D8486

Signed-off-by: Algent Albrahimi <algent@protonmail.com>

Test Plan: Check for errors in pythons scripts located in mypy/test-data/samples/ and then run thonny.

Reviewers: Triage Team, DataDrake

Reviewed By: Triage Team, DataDrake

Subscribers: DataDrake

Differential Revision: https://dev.getsol.us/D8488