DEP11 Validator: Allow some new types to not have package associations
Hi! The "operating-system" and "repository" component types have recently been added to AppStream, and both don't necessarily have to have a package associated with them. This change adjusts dak's DEP11 validator to recognize that and not fail in case one of those components shows up. A separate patch also changes the Python string notations in the validator script to be the same, the previous mix looked a bit odd. That is purely a style change without any functional impact.