Bump pymdown-extensions from 8.2 to 9.0

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 8.2 to 9.0.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](https://github.com/facelessuser/pymdown-extensions/compare/8.2...9.0)

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

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

docs/requirements.txt

@@ -9,4 +9,4 @@ mkdocs-minify-plugin==0.4.1
 mkdocs-redirects==1.0.3
 mkdocs==1.2.2
 pygments==2.10.0
-pymdown-extensions==8.2
+pymdown-extensions==9.0