Always make the dummy job give a warning and remove default assignees from new jO template

Changes introduced

With the new approval procedure:

• remove default assignees from new jO template
• make the dummy CI job always fail giving a warning (allowed to fail)

Tests

Let's see what happens...

https://gitlab.cern.ch/atlas-physics/pmg/mcjoboptions/-/jobs/16592123

And as you can see below the pipeline is yellow - when it will be merged in the master dummy should not run and the pipeline should be green.

Issues resolved

Closes #