Bump league/commonmark from 2.5.3 to 2.6.0 in /api (#12232)

Bumps [league/commonmark](https://github.com/thephpleague/commonmark) from 2.5.3 to 2.6.0.
- [Release notes](https://github.com/thephpleague/commonmark/releases)
- [Changelog](https://github.com/thephpleague/commonmark/blob/2.6/CHANGELOG.md)
- [Commits](thephpleague/commonmark@2.5.3...2.6.0)

---
updated-dependencies:
- dependency-name: league/commonmark
  dependency-type: indirect
...

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