Comment 9 for bug 1977493

I'm going to mark this triaged for ubuntu-release-upgrader. It's important to have guards in preinst scripts against breaking a system as part of an upgrade, but we also want to avoid actually hitting these failures in the middle of a release upgrade precisely because it's so difficult to get the system back into a coherent state afterwards. Where we know such preinst checks exist (especially for such critical packages as pam), it's best to have do-release-upgrader detect early and block the upgrade.