DiscoverWindow: Always show refresh action on desktop
Previously, we hid it when not in wideScreen mode, but this is an insufficient heuristic for determining whether we're on mobile and the user can pull down on the view to refresh instead. On desktop, a user cannot do this.
I cannot test this on mobile, so it should be tested, though I expect it should work as Kirigami.Settings.isMobile is already used to determine the global toolbar style.