Bump mypy from 0.761 to 0.770

Bumps [mypy](https://github.com/python/mypy) from 0.761 to 0.770.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.761...v0.770)

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

Author: dependabot-preview[bot]

dev-requirements.txt

@@ -16,7 +16,7 @@ flake8-quotes==2.1.1  # Require single quotes
 flake8==3.7.9  # Lint
 freezegun==0.3.15
 isort==4.3.21  # Lint imports
-mypy==0.761  # Type checking
+mypy==0.770  # Type checking
 pip-check-reqs-pip-gte-20==2.0.3.1
 pydocstyle==5.0.2  # Lint docstrings
 pyenchant==3.0.1  # Bindings for a spellchecking sytem