Bump pymdown-extensions from 10.3.1 to 10.9

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.3.1 to 10.9.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](facelessuser/pymdown-extensions@10.3.1...10.9)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements-2.9.txt

@@ -182,7 +182,7 @@ pymacaroons==0.13.0
     #   -r requirements.in
     #   macaroonbakery
     #   surl
-pymdown-extensions==10.3.1
+pymdown-extensions==10.9
     # via mkdocs-material
 pynacl==1.5.0
     # via