Tab scroll arrow should be clickable

When viewing on a normal screen, but with new UI enabled (thus a left sidebar), and some discussions, the merge request page shows the tabs (Discussion, Commits, Pipelines, Changes) in a horizontally scrollable region. Whenever I see this, I expect to be able to click on the arrow indicating scrollable content and then I spend a chunk of time trying to click on it and any other click target I see around it, before I remember that I can scroll.

An example confirmed as bug in 2017-08, which is no more a bug in 2022-08

Another example confirmed as bug in 2022-08

Adapted from !94464 (merged)