Include author in assignee dropdown search

## What does this MR do?

Previously when you searched for the author in the assignee dropdown (if they aren't in the project) it did not actually include the author. This changes that so that when you search for the author it will correctly include the user.

## Screenshots (if relevant)

![Screen_Shot_2016-11-17_at_11.14.53](/uploads/5a13475d8ded459fd3b1ba6570897665/Screen_Shot_2016-11-17_at_11.14.53.png)

## What are the relevant issue numbers?

Closes #22905

See merge request !7526