Unable to make "Assignee" non-editable in NewIssueView

Issue Summary

In New Issue View, even if we remove the “Assignee” field from “Edit Screen”, users having “Assign Issue” permission are able to change the Assignee.

Steps to Reproduce

1. Remove "Assignee" from the "Edit Screen"
2. Associate "Assign Issue" project permission with "Any Logged-in users"

Expected Results

No user should be allowed to edit the Assignee field.

Actual Results

Any user who is logged in to the instance is able to edit Assignee

Workaround

How to restrict the assignment of issues that are already assigned to someone