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.

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

We need to have feature specs completely covering every aspect of interaction that exists with the label dropdown, be it by mouse or keyboard, and in every configuration and order of added/removed/intermediate labels. Everything a user could do to the dropdown in the browser should have a feature spec, because obviously the dropdown is complex and manual validation in the browser is not cutting it.

/cc @alfredo1

!4781 (merged) fixed this when it appeared a couple months ago but other dropdown fixes have been merged before it so there are conflicts on that branch again, I'll see to it this week.

This MR also introduces a spec that I will try to flesh out some more.

I'll make a lot more noise when its ready to merge this time.

@lbennett great! if we can have it done by tomorrow in the am that would be great and will let us release the RC 2 of 8.11 to production :)

mentioned in merge request !4781 (merged)

@jschatz1 This needs to be fixed for 8.11.

@rspeicher I thought someone (maybe @iamphill) fixed this recently? If not there is a fix in !4781 (merged)... but again, specs, specs that wont be complete for a while, I'd be impressed if they can be squeezed into %8.12.

Reassigned to @jschatz1

mentioned in merge request !5870 (closed)

Status changed to closed by commit b06f9211

Status changed to closed by merge request !4781 (merged)

mentioned in commit b06f9211

mentioned in commit 9510073d

Mentioned in commit nick.thomas/gitlab-ee@9510073d

mentioned in merge request !14785