Infinite Email Loop When Assigning Task via GitHub Integration

### Description of the issue
When a task is assigned to a user via our GitHub integration, the assigned user receives an infinite loop of emails. The same email is sent repeatedly, creating a flood of notifications for the assigned user.

### Steps to reproduce
1. Assign a task to a user using the GitHub integration.
2. Observe the emails received by the assigned user.

### Expected behaviour
The assigned user should receive only one email notifying them of the task assignment.

### Actual behaviour
The assigned user is receiving continuous, repeated emails for the same task assignment, instead of a single notification.

### Possible solutions
The issue might be caused by a loop in the notification system or an unintended retry mechanism. A solution could involve investigating the email notification logic and ensuring the task assignment sends only one email notification per assignment.

Start by reproducing the task assignment through the GitHub integration and trace the email notification entry point and any retry path. Confirm the repeated messages for one assignment, then verify that the assigned user receives only one notification for that assignment.

Written by the indexing model from the issue text.