Update mypy requirement from >=0.991,<1.6 to >=0.991,<1.8

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@v0.991...v1.7.0)

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

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

pyproject.toml

@@ -19,7 +19,7 @@ httpx = ">=0.23.1,<0.26.0"
 isort = "^5.7.0"
 mkdocs-material = ">=8.3.9,<10.0.0"
 pylint = ">=2.6.2,<4.0.0"
-mypy = ">=0.991,<1.6"
+mypy = ">=0.991,<1.8"
 pytest = "^7.0"
 pytest-cov = ">=3,<5"
 requests = "^2.25.1"