Update pytest requirement from >=3.6 to >=9.1.1

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@3.6.0...9.1.1)

---
updated-dependencies:
- dependency-name: pytest
  dependency-version: 9.1.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -4,7 +4,7 @@ h5py>=2.7
 scipy>=0.16
 numba
 
-pytest>=3.6
+pytest>=9.1.1
 nbval>=0.9.0
 pytest-cov>=2.6.0