Update the mypy and GitPython pip modules that are required for linting
builds before commits to compatible versions rather than hard version
requirements.
(cherry picked from commit ca4df25002)
The version of mypy we were depending on was very old and was causing a
version conflict on typed-ast with another module. On newer pip versions,
the result was a *very* slow process of walking back compatible versions
of multiple packages. This change updates mypy to the latest version
available.
(cherry picked from commit e4bd2ae1c3)