chore(deps-dev): bump next-sitemap from 4.1.3 to 4.1.8 in /docs

Bumps [next-sitemap](https://github.com/iamvishnusankar/next-sitemap) from 4.1.3 to 4.1.8.
- [Release notes](https://github.com/iamvishnusankar/next-sitemap/releases)
- [Changelog](https://github.com/iamvishnusankar/next-sitemap/blob/master/changelog.md)
- [Commits](iamvishnusankar/next-sitemap@4.1.3...4.1.8)

---
updated-dependencies:
- dependency-name: next-sitemap
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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