Fix versions not being flagged for review after 2nd level approval requeue

[diox]

Fixes mozilla/addons#15822

Description

This refactors how versions are passed when flagging for review in CinderAddonHandledByReviewers, always passing down a Version queryset.

Context

We were expecting version strings in flag_for_human_review() (which is inefficient and confusing) but the requeue method was passing a Version queryset directly.

Later inside flag_for_human_review() there was a fallback that worked for the listed channel that caused us to flag the current_version (with further handling for the case where it's an appeal and there is no current_version anymore). But for unlisted, nothing, so we didn't flag anything.

Testing

• Enable all DSA waffle switches
• Submit an add-on as unlisted (do not have a listed version!)
• Make that add-on promoted so that negative decisions are held for 2nd level approval
• Force-disable that add-on - the decision should be held for 2nd level approval
• In second level approval, requeue the decision

Expected result:

• You should see that add-on in the reviewer queue ; in the review page, the version should be flagged as needing human review, there should be an activity log explaining that it was requeued, and the version should have a due date

Actual result before this patch:

• None of that ^^