chore(deps-dev): bump mypy from 0.920 to 0.921

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
...

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

Author: dependabot[bot]

poetry.lock

@@ -53,7 +53,7 @@ flake8-bugbear = "^21.11.29"
 mkdocs-material = "^7.3.6"
 mkdocs-git-revision-date-plugin = "^0.3.1"
 mike = "^0.6.0"
-mypy = "^0.920"
+mypy = "^0.921"
 
 
 [tool.poetry.extras]