Update pytest requirement in /.dev in the python group (#741)

Updates the requirements on [pytest](https://github.com/pytest-dev/pytest) to permit the latest version.

Updates `pytest` to 9.1.0
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@9.0.0...9.1.0)

---
updated-dependencies:
- dependency-name: pytest
  dependency-version: 9.1.0
  dependency-type: direct:development
  dependency-group: python
...

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.dev/requirements_dev.txt

@@ -3,7 +3,7 @@ fakeredis~=2.36
 httpx~=0.28.1
 invoke~=3.0
 pre-commit~=4.6
-pytest~=9.0
+pytest~=9.1
 pytest-cov~=7.1
 
 # httpx is necessary due to the use of fastapi/starlette's TestClient