build(deps-dev): bump github-markdown-css from 5.8.1 to 5.9.0

Bumps [github-markdown-css](https://github.com/sindresorhus/github-markdown-css) from 5.8.1 to 5.9.0.
- [Release notes](https://github.com/sindresorhus/github-markdown-css/releases)
- [Commits](sindresorhus/github-markdown-css@v5.8.1...v5.9.0)

---
updated-dependencies:
- dependency-name: github-markdown-css
  dependency-version: 5.9.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

package-lock.json

@@ -16,7 +16,7 @@
     "concurrently": "^9.2.1",
     "express": "^5.2.1",
     "fast-glob": "^3.3.3",
-    "github-markdown-css": "^5.8.1",
+    "github-markdown-css": "^5.9.0",
     "handlebars": "^4.7.8",
     "showdown": "^2.1.0",
     "showdown-footnotes": "^2.1.2",