Bump mypy from 0.931 to 0.940 (#292)

Bumps [mypy](https://github.com/python/mypy) from 0.931 to 0.940.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.931...v0.940)

---
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/ci.txt

@@ -1,5 +1,5 @@
 setuptools-git==1.2
-mypy==0.931; implementation_name=="cpython"
+mypy==0.940; implementation_name=="cpython"
 mypy-extensions==0.4.3; implementation_name=="cpython"
 
 -r ci-wheel.txt