Bump mypy from 0.920 to 0.921 (#419)

Bumps [mypy](https://github.com/python/mypy) from 0.920 to 0.921.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.920...v0.921)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -21,7 +21,7 @@ flake8-simplify = "^0.14.2"
 flake8-use-fstring = "^1.3"
 homeassistant-stubs = "2021.11.0"
 isort = "^5.10.1"
-mypy = "^0.920"
+mypy = "^0.921"
 pre-commit = "^2.16.0"
 pylint = "^2.12.2"
 codespell = "^2.1.0"