Adding fudge points doesn't update "graded_at" in the submissions API

[#1]

This change is noted in Canvas Deploy Notes (2021-02-17) - Canvas Community

Description

When a teacher adds fudge points to a quiz grade and saves, the "graded_at" object in the submissions API doesn't update.

Expected Behavior

Instead, "graded_at" should be updated anytime something about the submission grade is updated.

Steps to Reproduce

Prerequisites: Have a quiz with at least one submission.

1. Look in the submissions API and see a specific "graded_at" date.
2. In speed grader, add fudge points to the submission and save.
3. Refresh the submissions API and see that "graded_at" has stayed the same.

Additional Info

QUIZ-7898