Bump matplotlib from 3.8.2 to 3.9.1

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.8.2 to 3.9.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.2...v3.9.1)

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

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

docs/requirements.txt

@@ -34,7 +34,7 @@ kiwisolver==1.4.5
     # via matplotlib
 markupsafe==2.1.3
     # via jinja2
-matplotlib==3.8.2
+matplotlib==3.9.1
     # via -r requirements.in
 numpy==1.26.4
     # via