title tooltips with same text as existing one don't show

A minor oddity, but different from Chromium nonetheless:

When going to e.g. https://www.uplawski.eu/france/Normandie/ with simplebrowser and hovering the first picture, its tooltip "Charolaises" is shown. When then hovering over the second picture which has the same tooltip text, the old tooltip persists, and no new one is shown.

Doing the same in Chromium correctly hides the old tooltip and shows the new one.

Downstream report: https://github.com/qutebrowser/qutebrowser/issues/6945