Update mypy requirement from ^0.910 to ^0.920

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.910...v0.920)

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

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

pyproject.toml

@@ -25,7 +25,7 @@ pywikibot = "^6.6.1"
 toolforge = {version="^5.0.0", optional=true}
 
 [tool.poetry.dev-dependencies]
-mypy = "^0.910"
+mypy = "^0.920"
 flake8 = "^4.0.0"
 black = "^21.9b0"
 pytest = "^6.2.5"