Course.MultipleObjectsReturned: get() returned more than one Course -- it returned 2!

[sentry-io]

We started throwing this error suddenly on 7/8, probably due to data in production, and not due to a code change.

We often have to create course runs in the db before a course key is available. Queries on course runs shouldn't expect a unique course key.

We should add some tests that exercise this condition.

Sentry Issue: MICROMASTERS-582

Course.MultipleObjectsReturned: get() returned more than one Course -- it returned 2!
(5 additional frame(s) were not displayed)
...
  File "dashboard/api.py", line 274, in <listcomp>
    run_statuses = [get_status_for_courserun(course_run, mmtrack)
  File "dashboard/api.py", line 399, in get_status_for_courserun
    if mmtrack.has_paid(course_run.edx_course_key):
  File "dashboard/utils.py", line 222, in has_paid
    course = Course.objects.get(courserun__edx_course_key=edx_course_key)
  File "django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "django/db/models/query.py", line 410, in get
    raise self.model.MultipleObjectsReturned(

An exception was intercepted by custom_exception_handler