Prevent translations that fail the automated tests from being merged into tails/master

Since a while there are several automated tests triggered by merges from the translation platform.

It is very nice to receive an alert when these checks fail. But you know what would be better? To not merge those commits that fail the tests!

Prioritization by RM

• Such problems can lead to stressful last minute issues during releases. They are always solvable, but it would be best dealt before the release process starts.
• Medium priority in terms of expected benefits from RM point of view. Only Zen Fu can tell whether cost/benefit is good.