Bump pytest-mypy from 0.8.0 to 0.9.1

Bumps [pytest-mypy](https://github.com/dbader/pytest-mypy) from 0.8.0 to 0.9.1.
- [Release notes](https://github.com/dbader/pytest-mypy/releases)
- [Changelog](https://github.com/dbader/pytest-mypy/blob/master/changelog.md)
- [Commits](realpython/pytest-mypy@v0.8.0...v0.9.1)

---
updated-dependencies:
- dependency-name: pytest-mypy
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Pipfile

@@ -18,5 +18,5 @@ pytest-aiohttp = "==0.3.0"
 pytest-cov = "==3.0.0"
 pytest-mock = "==3.6.1"
 pytest-flake8 = "==1.0.6"
-pytest-mypy = "==0.8.0"
+pytest-mypy = "==0.9.1"
 pytest-isort = "==1.2.0"