Update troubleshooting-404-errors-for-github-pages-sites.md

[Yuchen-Song]

Why: Added troubleshooting for Github Page 404 error with private repository of an expired GitHub Pro, GitHub Team, GitHub Enterprise Cloud,or GitHub Enterprise Server user.

Closes: https://github.com/orgs/community/discussions/36070

What's being changed (if available, include any code snippets, screenshots, or gifs): Added one line in the doc

* Check if your GitHub Pro, GitHub Team, GitHub Enterprise Cloud, or GitHub Enterprise Server access has expired if you are using a private repository for the Github Page Site. If so, please make sure to renew it or change your repository's visibility to public.

Check off the following:

• [x] I have reviewed my changes in staging, available via the View deployment link in this PR's timeline (this link will be available after opening the PR).

  • For content changes, you will also see an automatically generated comment with links directly to pages you've modified. The comment won't appear if your PR only edits files in the data directory.

• [x] For content changes, I have completed the self-review checklist.