Update list-of-update-sites page

The `list-of-update-sites` repository is still styled after the old MediaWiki.

We need to integrate this better with the new wiki.

* At minimum: that means updating the style to match the new site.
* But maybe better would be to migrate the `sites.yml` to this repository instead, and integrate it into the GitHub Actions. Then we wouldn't need to copy-paste the page style from `_includes/page` to the `list-of-update-sites` repository, but rather would benefit from it being more DRY here.

Possibly, the two above points should be two issues... for now, this issue exists as a reminder to evaluate how we want to proceed.

Start by comparing the list-of-update-sites repository with the new wiki and the styling in _includes/page. Evaluate whether to update the copied style or migrate sites.yml into this repository and integrate it with GitHub Actions. Done means an agreed approach is implemented without the current copy-paste styling.

Written by the indexing model from the issue text.