Bump mypy from 0.990 to 0.991 (#270)

Bumps [mypy](https://github.com/python/mypy) from 0.990 to 0.991.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.990...v0.991)

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

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requirements_dev.txt

@@ -3,7 +3,7 @@ black==22.10.0
 coverage==6.5.0
 flake8==5.0.4
 lxml==4.9.1
-mypy==0.990
+mypy==0.991
 pylint==2.15.5
 pytest==7.2.0
 pytest-asyncio==0.20.2