Resolve "Fix "cannot merge" icon alignment in assignees widget dropdown"

What does this MR do and why?

This MR fixes the positioning of "cannot merge" icon on the assignees widget dropdown

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. In rails console enable the feature flag for assignees wdget

   Feature.enable(:issue_assignees_widget)

2. Visit any merge request page.
3. Open the Assignees dropdown on the sidebar.
4. Try to assign to project members that cannot merge

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #413437 (closed)