Bump katex from 0.16.11 to 0.16.21

Bumps [katex](https://github.com/KaTeX/KaTeX) from 0.16.11 to 0.16.21.
- [Release notes](https://github.com/KaTeX/KaTeX/releases)
- [Changelog](https://github.com/KaTeX/KaTeX/blob/main/CHANGELOG.md)
- [Commits](https://github.com/KaTeX/KaTeX/compare/v0.16.11...v0.16.21

)

---
updated-dependencies:
- dependency-name: katex
  dependency-type: direct:production
...

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