My Due Tasks panel doesn't display tasks with multiple assignees

[abrassat]

Describe the bug
The My Due Tasks panel doesn't display assigned tasks, if the task has multiple assignees

Steps to reproduce
Steps to reproduce the problematic behavior:

1. Create a task with assignees Admin,User1
2. As Admin, visit the TaskManager space
3. Observe the My Due Tasks panel on the right side of the page

Expected behavior
The task with assignees Admin,User1 is visible in the panel

Actual behavior
The task with assignees Admin,User1 is not visible in the panel

Environment (please complete the following information):

• OS: linux mint
• Browser firefox
• XWiki version 15.10
• App version 3.11.0

Additional context
Add any other context about the problem here.