Bump dompurify and mermaid in /docs

Bumps [dompurify](https://github.com/cure53/DOMPurify) and [mermaid](https://github.com/mermaid-js/mermaid). These dependencies needed to be updated together.

Updates `dompurify` from 3.1.6 to 3.2.5
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](cure53/DOMPurify@3.1.6...3.2.5)

Updates `mermaid` from 11.4.0 to 11.6.0
- [Release notes](https://github.com/mermaid-js/mermaid/releases)
- [Changelog](https://github.com/mermaid-js/mermaid/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/mermaid-js/mermaid/compare/mermaid@11.4.0...mermaid@11.6.0)

---
updated-dependencies:
- dependency-name: dompurify
  dependency-version: 3.2.5
  dependency-type: indirect
- dependency-name: mermaid
  dependency-version: 11.6.0
  dependency-type: indirect
...

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Author: dependabot[bot]