chore(deps-dev): bump @vuepress/plugin-shiki

Bumps [@vuepress/plugin-shiki](https://github.com/vuepress/vuepress-next) from 2.0.0-beta.59 to 2.0.0-beta.60.
- [Release notes](https://github.com/vuepress/vuepress-next/releases)
- [Changelog](https://github.com/vuepress/vuepress-next/blob/main/CHANGELOG.md)
- [Commits](vuepress/core@v2.0.0-beta.59...v2.0.0-beta.60)

---
updated-dependencies:
- dependency-name: "@vuepress/plugin-shiki"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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