Some users are duplicated in Issue assignees search results

Summary

When searching for project members on issue assignees dropdown, a few members are duplicated. This might be a result of searching in relations to [DIRECT, INHERITED, INVITED_GROUPS] (adding the latter causes the duplication)

Steps to reproduce

1. Open any issue on gitlab.org/gitlab
2. Open assignees dropdown on the right side
3. Search for @ntepluhina

What is the current bug behavior?

User is displayed twice

What is the expected correct behavior?

Unique user should be only displayed once

Relevant logs and/or screenshots

Possible fixes

backend should return a list of users without duplications. As a temporary measure, frontend can remove duplicated with filtering the search results