Build(deps): Bump matplotlib from 3.8.0 to 3.9.1 in /requirements

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.8.0 to 3.9.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.0...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>

Author: dependabot[bot]

requirements/requirements_doc.txt

@@ -3,7 +3,7 @@ git+https://github.com/ansys/pyaedt@main
 
 # Examples dependencies
 imageio==2.34.0
-matplotlib==3.8.0
+matplotlib==3.9.1
 numpy==1.26.4
 openpyxl==3.1.4
 osmnx==1.9.0