spec: fix content_migrations_spec for draft state

closes #CNVS-14302

Change-Id: Ie9850318290620da22a37b44fe151b3f36079b8f
Reviewed-on: https://gerrit.instructure.com/38264
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>