Update mypy requirement from ~=1.5.1 to ~=1.6.0

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Commits](python/mypy@v1.5.1...v1.6.0)

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

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

requirements-dev.txt

@@ -7,7 +7,7 @@ django-stubs-ext~=4.2.0
 django-webtest~=1.9.10
 isort~=5.12.0
 model-bakery~=1.15.0
-mypy~=1.5.1
+mypy~=1.6.0
 openpyxl-stubs~=0.1.25
 pylint-django~=2.5.3
 pylint~=2.17.1