Do not allow start message job to fail
What does this MR do and why?
Describe in detail what your merge request does and why.
Content
- Do not allow start message job to fail
By default, manual jobs are allowed to fail (https://docs.gitlab.com/ee/ci/yaml/#allow_failure). In this situation, we don't want that, since we don't want to let a rake task runs without sending a Slack notification.