avoid re-touching course in enrollment grade calculator
avoid re-touching course in enrollment grade calculator

should help with many concurrent recalculation jobs for a
single course

closes #CNVS-32173

Change-Id: I0bb7e6e07dac06793fd0b00e46c85bb9583086e2
Reviewed-on: https://gerrit.instructure.com/91531
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

matematikk-mooc/canvas-lms,HotChalk/canvas-lms,matematikk-mooc/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,djbender/canvas-lms,matematikk-mooc/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,grahamb/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms