Leaderboard: close the evidence tooltip on scroll (#6)

44578fa rewrote the evidence tooltip from CSS :hover to JS
mouseenter/mouseleave and repositioned it while scrolling. Scrolling
never fires mouseleave, so the tooltip outlived its hover, followed its
anchor, and piled up until a page switch. Close it on scroll (capture)
instead; hover, focus and Escape paths are unchanged.

Co-authored-by: Khazix <wzglyay@gmail.com>