Support pressing arrow-up when choosing labels #1450

It's new feature proposal.

Scenario: I created pull request, and I'm adding labels. I want to add label Please CR: JS. I type first two letters (Pl) into search input, and now I see 5 similar labels (e.g. Please CR: CSS, Please CR: HTML). The one that I'm looking for is at the very end. I'd like to navigate to this label by pressing up arrow. Unfortunately, nothing happens.

Feature proposal: During label searching, pressing up arrow at first item navigates me to the last one, and pressing down arrow at last item navigates me to the first item.