ci(deps): bump pymdown-extensions from 10.21.2 to 10.21.3

Bumps [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) from 10.21.2 to 10.21.3.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](facelessuser/pymdown-extensions@10.21.2...10.21.3)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-version: 10.21.3
  dependency-type: indirect
...

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

Author: dependabot[bot]