Use h2 for Completion Prerequisites header
Use h2 for Completion Prerequisites header

Test plan:
  - Create two modules, each with assignments
  - Make the first module the prerequisite for the second
  - View an assignment in the second module as a student
  - "Completion Prerequisites" should be render using an h2

Fixes EVAL-2506

flag=none

Change-Id: I6df1061e382d6b3ad4d1c68b172c5f0e839f71ba
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/294049
Reviewed-by: Paulo Chaves <25f22fd35323c1b47bb3246c49aa4dd25a34bdf4@instructure.com>
Reviewed-by: Samuel Lee <921b9c93b549c38195942075229787818b5c5434@instructure.com>
Reviewed-by: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
QA-Review: Samuel Lee <921b9c93b549c38195942075229787818b5c5434@instructure.com>
Product-Review: Jody Sailor
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms