Mark job_explanation strings after they are read from the db

- For strings that need to be translated, but are saved in the db:
   * They must be marked for translation using gettext_noop() to be
   translated.
   * And must also be marked for translation with _() when read from db
   and shown to the user.
   * [Ref]: https://docs.djangoproject.com/en/3.0/topics/i18n/translation/#marking-strings-as-no-op

awx/main/tasks.py

@@ -31,7 +31,7 @@ from django.db.models.fields.related import ForeignKey
 from django.utils.timezone import now, timedelta
 from django.utils.encoding import smart_str
 from django.contrib.auth.models import User
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import ugettext_lazy as _, gettext_noop
 from django.core.cache import cache
 from django.core.exceptions import ObjectDoesNotExist
 
@@ -558,7 +558,8 @@ def awx_periodic_scheduler():
                 continue
             if not can_start:
                 new_unified_job.status = 'failed'
-                new_unified_job.job_explanation = "Scheduled job could not start because it was not in the right state or required manual credentials"
+                new_unified_job.job_explanation = gettext_noop("Scheduled job could not start because it \
+                    was not in the right state or required manual credentials")
                 new_unified_job.save(update_fields=['status', 'job_explanation'])
                 new_unified_job.websocket_emit_status("failed")
             emit_channel_notification('schedules-changed', dict(id=schedule.id, group_name="schedules"))