Hello,
This appears to be a bug created by our SkinConfig feature. What's happening is it is looking up the PageSettings to determine if the page has a skin set on it, that process is then trying to find the DraftApprovalRoles on the record but that column hasn't been added to the table yet.
All of this is happening because the SkinConfig is populated when the site starts. We might be able to change this in the upcoming release so this is skipped if you're browsing to the setup page. I'm not 100% on that right at the moment and we're literally writing the blog post for the next release (2.9.1), so I am hesitant to change that release at this point.
A workaround would be to upgrade to 2.7 and then to 2.9.0.1. SkinConfig didn't exist in 2.7 so you it will not be a problem.
Hope this helps,
Joe