gitlab-pages is easy to forget to update, and interacts badly with coverage

the gitlab pages for Arti says it's still 0.3, but 0.4 is available.
Updating the pages branch would cause coverage report to disappear (and reappear on next scheduled CI job). I think this branch should not exist, and the website should be directly on main. This would make the release process easier (only one branch to update), and would make the CI less strange in how deploying pages is done.