PrinterSettings: Fix progress bar color for ink levels
In KF6, qqc2-desktop-style no longer follows the palette. Furthermore, Breeze widget style uses the Accent color for its progress bar now, for which there is no equivalent in Kirigami.Theme.
Together with a change in Kirigami, setting the highlightColor makes the progress bar the right color again.
Needs frameworks/kirigami!1679 (merged) for the color to work