Package of the week section can end up with the same video twice

[sigurdm]

Happened today:

[isoos]

This seems to be a bug in the retry logic + cache of the fetching code:
https://github.com/dart-lang/pub-dev/blob/master/app/lib/service/youtube/backend.dart#L125-L133

We seem to re-populate the video list with the same cached page content.