Bump pymdown-extensions from 9.0 to 9.1

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 9.0 to 9.1.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](https://github.com/facelessuser/pymdown-extensions/compare/9.0...9.1)

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

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

docs/requirements.txt

@@ -9,4 +9,4 @@ mkdocs-minify-plugin==0.5.0
 mkdocs-redirects==1.0.3
 mkdocs==1.2.3
 pygments==2.10.0
-pymdown-extensions==9.0
+pymdown-extensions==9.1