Fix zone fill issue with net ties

A mistake in the cherry-pick for a previous commit prevented footprint
graphics from being knocked out in the zone fill.  This sets the default
to knockout, allowing the assertion from the polygon generation routine
to catch invalid codes

Fixes https://gitlab.com/kicad/code/kicad/-/issues/15069

pcbnew/zone_filler.cpp

@@ -879,14 +879,10 @@ void ZONE_FILLER::addKnockout( BOARD_ITEM* aItem, PCB_LAYER_ID aLayer, int aGap,
         break;
     }
 
-    case PCB_SHAPE_T:
-    case PCB_TARGET_T:
+    default:
         aItem->TransformShapeToPolygon( aHoles, aLayer, aGap, m_maxError, ERROR_OUTSIDE,
                                         aIgnoreLineWidth );
         break;
-
-    default:
-        break;
     }
 }