Bump pymdown-extensions from 10.17.1 to 10.20 (#510)

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.17.1 to 10.20.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](facelessuser/pymdown-extensions@10.17.1...10.20)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-version: '10.20'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]