Add a test that the title field of push notifications is required for every language that is a primary language of one of its regions

[david-venhoff]

Motivation

This is a new behavior that is currently untested. For more information see https://github.com/digitalfabrik/integreat-cms/pull/2727#pullrequestreview-1988730148

Proposed Solution

Add a test that checks this behavior

Alternatives

Add no test