Update mypy requirement from <1.8 to <1.9

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@v0.1.0...v1.8.0)

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

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

pyproject.toml

@@ -93,7 +93,7 @@ dependencies = [
 [project.optional-dependencies]
 develop = [
   "black<24",
-  "mypy<1.8",
+  "mypy<1.9",
   "poethepoet<0.25",
   "pyproject-fmt<1.6",
   "ruff==0.1.7",