Bump @docusaurus/plugin-content-docs from 3.8.1 to 3.9.1 in /docs

Bumps [@docusaurus/plugin-content-docs](https://github.com/facebook/docusaurus/tree/HEAD/packages/docusaurus-plugin-content-docs) from 3.8.1 to 3.9.1.
- [Release notes](https://github.com/facebook/docusaurus/releases)
- [Changelog](https://github.com/facebook/docusaurus/blob/main/CHANGELOG.md)
- [Commits](https://github.com/facebook/docusaurus/commits/v3.9.1/packages/docusaurus-plugin-content-docs)

---
updated-dependencies:
- dependency-name: "@docusaurus/plugin-content-docs"
  dependency-version: 3.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

docs/package.json

@@ -18,7 +18,7 @@
   },
   "dependencies": {
     "@docusaurus/core": "^3.7.0",
-    "@docusaurus/plugin-content-docs": "^3.6.3",
+    "@docusaurus/plugin-content-docs": "^3.9.1",
     "@docusaurus/preset-classic": "^3.7.0",
     "@docusaurus/theme-mermaid": "^3.6.3",
     "@inkeep/docusaurus": "^2.0.16",