New shared translation cannot be dismissed on a diverged one.

When a translation is diverged, the shared translation is still displayed under it to make it possible to revert to that translation. When this shared translation is updated in a different series, it can be considered a new suggestion for this translation and the translator might choose to favour it over the current diverged translation. Therefore it is only fair to treat this situation as a "message with new suggestion" and display the option to dismiss this suggestion anyway.

This all happens but selecting the option has no effect on the new shared message and remains visible. What most likely happens is that the dismissal updates the *shared* current translation's last_reviewed date but not that of the diverged one.