Fix ScrollArea redrawing every frame

The _requires_render property was not reset to False after rendering. This caused the UIScrollArea to re-render every frame.

Author: csd4ni3l

arcade/gui/experimental/scroll_area.py

@@ -326,6 +326,7 @@ def _do_render(self, surface: Surface, force=False) -> bool:
             self.do_render_base(surface)
             self.do_render(surface)
             self._rendered = True
+            self._requires_render = False
 
         return rendered