fix fragile course spec

my theory is that all the students had the same name, so the order they
were being returned in the csv was not deterministic.

fixes CNVS-16278

test plan:
- the spec should not fail intermittently

Change-Id: I99a1f1c223b7f308ccb08d2439e4175b20228c50
Reviewed-on: https://gerrit.instructure.com/45549
Reviewed-by: Cameron Sutter <csutter@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Simon Williams <simon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>