Bump mermaid from 8.13.6 to 8.13.8 in /docs (apollographql#2083)

Bumps [mermaid](https://github.com/knsv/mermaid) from 8.13.6 to 8.13.8.
- [Release notes](https://github.com/knsv/mermaid/releases)
- [Changelog](https://github.com/mermaid-js/mermaid/blob/develop/docs/CHANGELOG.md)
- [Commits](mermaid-js/mermaid@8.13.6...8.13.8)

---
updated-dependencies:
- dependency-name: mermaid
  dependency-type: indirect
...

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

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