Fix breaking change with job inputs when using invalid moa syntax

We have a breaking change currently in main that when no job inputs are defined and some keywords that are subject to job inputs interpolation contain invalid moa syntax the job fails. We don't want that. It's okay to fail the job if job inputs are defined, but not when there are none.

An example for a job definition that triggers the breaking change:

test:
  script:
    - echo $