chore(deps): Update mypy requirement from ~=1.5 to ~=1.6

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Commits](python/mypy@v1.5.0...v1.6.0)

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

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

requirements-testing.txt

@@ -4,7 +4,7 @@ pytest ~= 7.4
 pytest-cov ~= 4.1
 pytest-xdist ~= 3.3
 twine ~= 4.0
-mypy ~= 1.5
+mypy ~= 1.6
 black ~= 23.9
 ruff ~= 0.0.290
 moto[s3,sts] ~= 4.2