Bump dompurify and ngx-markdown in /desktop/angular

Bumps [dompurify](https://github.com/cure53/DOMPurify) to 3.1.6 and updates ancestor dependency [ngx-markdown](https://github.com/jfcere/ngx-markdown). These dependencies need to be updated together.


Updates `dompurify` from 2.4.3 to 3.1.6
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](cure53/DOMPurify@2.4.3...3.1.6)

Updates `ngx-markdown` from 16.0.0 to 18.0.0
- [Release notes](https://github.com/jfcere/ngx-markdown/releases)
- [Commits](jfcere/ngx-markdown@v16.0.0...v18.0.0)

---
updated-dependencies:
- dependency-name: dompurify
  dependency-type: indirect
- dependency-name: ngx-markdown
  dependency-type: direct:production
...

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