The playhead is redrawn as an overlay, so instead of a full region
redraw using `ARegionType.draw()`, at least an overlay only redraw using
`ARegion.draw_overlay()` needs to be triggered.
Any redrawing within a window is skipped if neither the screen, nor any
of its areas or regions are tagged for redraw. So since there are no
other areas or regions to be fully redrawn in this window, no redrawing
will happen. The screen needs to be tagged for redraw, which will skip
most drawing in this case, and just draw the overlays as wanted.
Pull Request: https://projects.blender.org/blender/blender/pulls/134579
05c6446c38