Staging pipeline should ensure that two builds of the same sha of the same repo do not appear in the drop

- [ ] This issue is blocking
- [ ] This issue is causing unreasonable pain

Assets from two or more different builds of the same repo of the same sha shouldn't appear in the drop. This happens when Maestro can't disambiguate what build flowed downstream. It's usually harmless, but could signify an issue where we could **theoretically** publish different nuget packages or assets than what flowed downstream into another repo. It's unlikely, but it could happen.

Key bit here is assets. If there are two builds but no assets from one of them, then this is still fine. It means that one didn't get assigned to a channel.