Bump mypy from 0.910 to 0.920 (#273)

Bumps [mypy](https://github.com/python/mypy) from 0.910 to 0.920.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.910...v0.920)

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

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

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

requirements.txt

@@ -1,7 +1,7 @@
 -e .
 build==0.7.0
 docutils==0.18.1
-mypy==0.910; implementation_name=="cpython"
+mypy==0.920; implementation_name=="cpython"
 pre-commit==2.16.0
 pytest==6.2.5
 pytest-asyncio==0.16.0