Fix T78192: Draw Face Sets tool not updating the viewport color

The draw face set tool always needs to redraw the nodes, but it only
needs the full update when in smooth mode because it moves the vertices.

Reviewed By: sergey

Maniphest Tasks: T78192

Differential Revision: https://developer.blender.org/D8108

source/blender/editors/sculpt_paint/sculpt.c

@@ -5284,6 +5284,7 @@ static void do_brush_action_task_cb(void *__restrict userdata,
 
   /* Face Sets modifications do a single undo push */
   if (data->brush->sculpt_tool == SCULPT_TOOL_DRAW_FACE_SETS) {
+    BKE_pbvh_node_mark_redraw(data->nodes[n]);
     /* Draw face sets in smooth mode moves the vertices. */
     if (ss->cache->alt_smooth) {
       SCULPT_undo_push_node(data->ob, data->nodes[n], SCULPT_UNDO_COORDS);