Bump katex in /doc in the npm_and_yarn group across 1 directory

Bumps the npm_and_yarn group with 1 update in the /doc directory: [katex](https://github.com/KaTeX/KaTeX).


Updates `katex` from 0.16.20 to 0.16.21
- [Release notes](https://github.com/KaTeX/KaTeX/releases)
- [Changelog](https://github.com/KaTeX/KaTeX/blob/main/CHANGELOG.md)
- [Commits](KaTeX/KaTeX@v0.16.20...v0.16.21)

---
updated-dependencies:
- dependency-name: katex
  dependency-type: indirect
  dependency-group: npm_and_yarn
...

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