chore(deps): Bump pymdown-extensions from 10.20.1 to 10.21

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.20.1 to 10.21.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](https://github.com/facelessuser/pymdown-extensions/commits/10.21)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-version: '10.21'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements.txt

@@ -10,6 +10,6 @@ mkdocs-material-extensions == 1.3.1
 mkdocs-minify-plugin == 0.8.0
 pip-audit == 2.10.0
 Pygments == 2.19.2
-pymdown-extensions == 10.20.1
+pymdown-extensions == 10.21
 PyOpenSSL == 25.3.0
 yamllint == 1.38.0