Bump mypy from 0.800 to 0.812

Bumps [mypy](https://github.com/python/mypy) from 0.800 to 0.812.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.800...v0.812)

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

Author: dependabot-preview[bot]

dev-requirements.txt

@@ -14,7 +14,7 @@ flake8==3.8.4  # Lint
 freezegun==1.1.0  # Freeze time in tests
 isort==5.7.0  # Lint imports
 keyring==22.3.0
-mypy==0.800 # Type checking
+mypy==0.812 # Type checking
 pip_check_reqs==2.1.1
 pydocstyle==5.1.1  # Lint docstrings
 pyenchant==3.2.0  # Bindings for a spellchecking sytem