Bump matplotlib from 3.8.0 to 3.9.2 in /docs

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.8.0 to 3.9.2.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.0...v3.9.2)

---
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]

docs/requirements.txt

@@ -4,7 +4,7 @@ sphinx-click==5.0.1
 myst_parser==4.0.0
 ghostscript==0.7
 opencv-python==4.8.1.78
-matplotlib==3.8.0
+matplotlib==3.9.2
 accessible-pygments==0.0.5 
 pydata-sphinx-theme==0.15.4
 sphinx-copybutton==0.5.2