Update pytest requirement from <8 to <9

Updates the requirements on [pytest](https://github.com/pytest-dev/pytest) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@1.0.0b3...8.0.0)

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

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

setup.py

@@ -76,7 +76,7 @@
               'typesystem<0.5',
           ],
           'test': [
-              'pytest<8',
+              'pytest<9',
               'pytest-cov<5',
           ],
       },