missing types for `initialOpenGroupIndex`

[ulivz]

• [x] I confirm that this is an issue rather than a question.

Bug report

Steps to reproduce

This issue is related to https://github.com/vuejs/vuepress/issues/3127, when you're using nested sidebar group, initialOpenGroupIndex by default the first subgroup is opened initially. You can change this using the initialOpenGroupIndex: Specify an index to open another subgroup or use -1 for no open group.

For the types of initialOpenGroupIndex is missing.

What is expected?

types should be correct and tsc server should pass type check.

What is actually happening?

types are missing:

Other relevant information

• Output of npx vuepress info in my VuePress project:

  System:
    OS: macOS 12.3
    CPU: (10) arm64 Apple M1 Max
  Binaries:
    Node: 16.19.1 - ~/.nvm/versions/node/v16.19.1/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 8.19.3 - ~/.nvm/versions/node/v16.19.1/bin/npm
  Browsers:
    Chrome: 110.0.5481.100
    Edge: Not Found
    Firefox: Not Found
    Safari: 15.4
  npmPackages:
    @vuepress/core:  1.9.8
    @vuepress/theme-default:  1.9.8
    vuepress:  1.9.8
  npmGlobalPackages:
    vuepress: Not Found