Bump matplotlib in the pip-version group across 1 directory

Bumps the pip-version group with 1 update in the / directory: [matplotlib](https://github.com/matplotlib/matplotlib).


Updates `matplotlib` from 3.8.4 to 3.9.0
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.4...v3.9.0)

---
updated-dependencies:
- dependency-name: matplotlib
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: pip-version
...

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

requirements/requirements-test.txt

@@ -1,4 +1,4 @@
-matplotlib==3.8.4
+matplotlib==3.9.0
 nglview==3.1.2
 numpy==1.26.4
 scikit-learn==1.5.0