Bump mypy from 0.790 to 0.812

Bumps [mypy](https://github.com/python/mypy) from 0.790 to 0.812.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](https://github.com/python/mypy/compare/v0.790...v0.812)

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

requirements-dev.txt

@@ -7,7 +7,7 @@ coveralls==3.0.0
 flake8==3.8.4
 flake8-type-annotations==0.1.0
 flake8-tidy-imports==4.2.1
-mypy==0.790
+mypy==0.812
 pytest==6.2.2
 pytest-asyncio==0.14.0
 pytest-cov==2.11.1