Fix milestone column description

Nick Leonardrequested to merge
559070-fix-milestone-column-desc into master

What does this MR do and why?

Fix milestone column description from "open and unassigned" to "open and assigned" to correctly describe the scope.

References

Screenshots or screen recordings

Before After
image.png

How to set up and validate locally

1 open any milestone

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #559070

Merge request reports