Bump mypy from 0.701 to 0.720

Bumps [mypy](https://github.com/python/mypy) from 0.701 to 0.720.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.701...v0.720)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements/local.txt

@@ -8,7 +8,7 @@ django-test-plus==1.2.1
 factory-boy==2.12.0  # https://github.com/FactoryBoy/factory_boy
 flake8==3.7.7  # https://github.com/PyCQA/flake8
 ipdb==0.12  # https://github.com/gotcha/ipdb
-mypy==0.701  # https://github.com/python/mypy
+mypy==0.720  # https://github.com/python/mypy
 psycopg2==2.8.2 --no-binary psycopg2  # https://github.com/psycopg/psycopg2
 pylint-celery==0.3  # https://github.com/PyCQA/pylint-celery
 pylint-django==2.0.9  # https://github.com/PyCQA/pylint-django