Fix unreadable text when searching in sidebar

We used to have a separate SUSPENDED_BG, but it got removed in the UI
refactor.

https://www.reddit.com/r/Anki/comments/1029gbw/is_anyone_else_with_2155_experience_way_to_bright/

qt/aqt/browser/sidebar/tree.py

@@ -303,7 +303,7 @@ class SidebarTreeView(QTreeView):
     ) -> None:
         if self.current_search and (item := self.model().item_for_index(idx)):
             if item.is_highlighted():
-                brush = QBrush(theme_manager.qcolor(colors.STATE_SUSPENDED))
+                brush = QBrush(theme_manager.qcolor(colors.HIGHLIGHT_BG))
                 painter.save()
                 painter.fillRect(options.rect, brush)
                 painter.restore()