* Persist worker_name after job is finished
Persisting the worker_name on the job object in Redis would allow for debugging and
analyzing logs from the worker
* Remove redundent job.save() method call
* Remove check for null worker
Now that worker name is persisted after job finishes or fails,
no need to assert that worker name is None
* Change github runner to Ubuntu 20.04
* Change github runner to Ubuntu 20.04