Keyboard navigation for the label dropdown has an off-by-one error

  1. Press l to open the label dropdown
  2. Press three times
  3. Press Enter

The label above the selected label is checked.

labels-off-by-one

How many bugs related to the dropdowns are going to have to be filed before we decided that testing them is probably a good idea?

Discovered on staging.gitlab.com after 8.11 RC1 was deployed there.

cc @jschatz1 @iamphill @DouweM @stanhu