Update pytest-mypy requirement from ==0.8.1 to ==0.10.3

Updates the requirements on [pytest-mypy](https://github.com/dbader/pytest-mypy) to permit the latest version.
- [Release notes](https://github.com/dbader/pytest-mypy/releases)
- [Changelog](https://github.com/realpython/pytest-mypy/blob/v0.10.3/changelog.md)
- [Commits](realpython/pytest-mypy@v0.8.1...v0.10.3)

---
updated-dependencies:
- dependency-name: pytest-mypy
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

pyproject.toml

@@ -56,7 +56,7 @@ boto3 = ">=1.9.71,<2.0.0"
 coverage = ">=4.4"
 jsonpickle = ">1.4.1"
 pytest-cov = ">=2.4.0"
-pytest-mypy = "==0.8.1"
+pytest-mypy = "==0.10.3"
 mypy = "==0.910"