fix draft state module student progression overflow scrolling

test plan:
* create a course with draft state enabled
* create several students (enough so that visiting the
 module student progressions page, '/courses/X/modules/progressions',
 fills the list of students on the right-hand side
* all of the students should now be accessible with a scroll-bar,
 rather than hidden

fixes #CNVS-11847

Change-Id: If93766d06ace89f6d490a69fdb5ea53d66a01486
Reviewed-on: https://gerrit.instructure.com/32044
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>