build(deps): bump @docusaurus/preset-classic in /website (#2834)

Bumps [@docusaurus/preset-classic](https://github.com/facebook/docusaurus/tree/HEAD/packages/docusaurus-preset-classic) from 2.0.0-beta.18 to 2.0.0-beta.20.
- [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/v2.0.0-beta.20/packages/docusaurus-preset-classic)

---
updated-dependencies:
- dependency-name: "@docusaurus/preset-classic"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

website/package.json

@@ -15,7 +15,7 @@
     },
     "dependencies": {
         "@docusaurus/plugin-client-redirects": "2.0.0-beta.20",
-        "@docusaurus/preset-classic": "2.0.0-beta.18",
+        "@docusaurus/preset-classic": "2.0.0-beta.20",
         "@mdx-js/react": "^1.6.22",
         "clsx": "^1.1.1",
         "postcss": "^8.4.13",