Remove btn-group class from listbox helper

What does this MR do and why?

• Removes btn-group class from the listbox helper classlist to fix border radius
• Adds btn-group in instances when needed

Screenshots or screen recordings

	Before	After
http://127.0.0.1:3000/explore/groups
http://127.0.0.1:3000/dashboard/groups
http://127.0.0.1:3000/gitlab-org/gitlab-test/-/milestones
(no change) http://127.0.0.1:3000/gitlab-org/gitlab-test/-/forks
http://127.0.0.1:3000/gitlab-org/gitlab-test/-/starrers
http://127.0.0.1:3000/admin/users
(no change) http://127.0.0.1:3000/gitlab-org/gitlab-test/-/merge_requests
http://127.0.0.1:3000/gitlab-org/gitlab-test/-/labels

How to set up and validate locally

✂️ UX Paper Cuts 16.7 → Project page (#430244 - closed)

✂️ UX Paper Cuts 16.8 → Accessibility (#424396 - closed)