Update mypy requirement from >=1.2.0 to >=1.20.2 (#988)

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md)
- [Commits](python/mypy@v1.2.0...v1.20.2)

---
updated-dependencies:
- dependency-name: mypy
  dependency-version: 1.20.2
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Casper Nielsen <casper@diagrid.io>
Co-authored-by: Sam <sam@diagrid.io>

Author: 3 people

dev-requirements.txt

@@ -1,4 +1,4 @@
-mypy>=1.2.0
+mypy>=1.20.2
 mypy-extensions>=0.4.3
 mypy-protobuf>=2.9
 tox>=4.3.0