Resolve "Schedules are blocked by manual action"

This is tricky. If we're not using rules, then manual actions are by default not blocking. I think this is for backward compatibility.

In the doc for allow_failure:

allow_failure allows a job to fail without impacting the rest of the CI suite. The default value is false, except for manual jobs.

And in when:manual:

If you want to make manual action blocking, it is necessary to add allow_failure: false to the job’s definition in .gitlab-ci.yml.

However given the new feature, manual actions are blocking by default, therefore we need to set allow_failure to true to make it non-blocking. This wasn't clear in the documentation and I cannot find it anywhere in rules

I think making it blocking makes more sense, but that's not how we used to use so we're not familiar with that yet.

Closes #351 (closed)