chore(deps): bump @docusaurus/preset-classic in /testsite

Bumps [@docusaurus/preset-classic](https://github.com/facebook/docusaurus/tree/HEAD/packages/docusaurus-preset-classic) from 3.0.1 to 3.1.0.
- [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/v3.1.0/packages/docusaurus-preset-classic)

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

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