Bump mkdocs-material from 9.5.23 to 9.5.39 in /docs

Bumps [mkdocs-material](https://github.com/squidfunk/mkdocs-material) from 9.5.23 to 9.5.39.
- [Release notes](https://github.com/squidfunk/mkdocs-material/releases)
- [Changelog](https://github.com/squidfunk/mkdocs-material/blob/master/CHANGELOG)
- [Commits](squidfunk/mkdocs-material@9.5.23...9.5.39)

---
updated-dependencies:
- dependency-name: mkdocs-material
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

docs/requirements.txt

@@ -1,4 +1,4 @@
-mkdocs-material==9.5.23
+mkdocs-material==9.5.39
 mkdocs-macros-plugin==1.0.5
 mkdocs-awesome-pages-plugin==2.9.2
 mkdocs-exclude==1.0.2