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-version: 0.16.21
  dependency-type: direct:development
...

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

package.json

@@ -56,7 +56,7 @@
     "imagesloaded": "^5.0.0",
     "include-media": "^1.4.10",
     "ityped": "^1.0.3",
-    "katex": "^0.16.11",
+    "katex": "^0.16.21",
     "mark.js": "^8.11.1",
     "mermaid": "^9.2.1",
     "plyr": "^3.7.2",