#122114 guarded mark_job_run/claim paths against a hand-edited
"completed": null, but update_job and the job_definition merge still used
.get("completed", 0), which returns None when the key is present, so the
null was carried forward into the store. Use `or 0` there too, and pin the
behaviour with one test covering mark_job_run and update_job.
Fixes#123281
Co-authored-by: John Paul Soliva <soliva.johnpaul@icloud.com>
Co-authored-by: JoaoMarcos44 <joaomarcosdias444@gmail.com>
Co-authored-by: mochamgx <1114149@qq.com>