spec: fix race condition in module item cache test

fixes CNVS-11961

Change-Id: I668318ec150b17625187ad01deb09a66567bb34e
Reviewed-on: https://gerrit.instructure.com/32229
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>