D2L Creating Duplicate Grade Items for an Assignment After Grade Sync

## Bug report form
### Steps to reproduce
Unable to reproduce. Issue happens randomly. Below is what the affected user from CCC has observed.
1. Certain Hypothesis assignments, with auto-grading enabled, initially has no grade item associated with it.
2. Instructor syncs grades from the LMS dashboard.
3. Instructor noticed that the gradebook now has two columns that correspond to the assignment. One is completely blank and the other reflects the grades synced from the LMS dashboard.
4. Inspecting the assignment again, it now has two identical grade items associated with it.

### Expected behaviour
Only one grade item will be created after the grade sync.

### Actual behaviour
Two identical grade items were created and associated with the assignment.

### Additional details

- Issue happens on certain newly created assignments and copied assignments.
- Auto-create grade items is enabled for the Hypothesis install (Application Instance 6533).
- One of the affected assignments: `Assignment ID: 475929` - `Demonstration 14.A - The Surprising Neuroscience of Gender Inequality | Janet Crawford | TEDxSanDiego`
- Here's a screenshot showing that the same LTI created the grade item for the Demonstration 14.A assignment twice.

Related Hubspot ticket: https://app.hubspot.com/contacts/6291320/record/0-5/26943090522