Fix #113142: Sculpt fairing operators don't update normals

Tagging the PBVH nodes isn't enough, each vertex has to be tagged too.

source/blender/editors/sculpt_paint/sculpt_face_set.cc

@@ -1203,6 +1203,7 @@ static void sculpt_face_set_edit_fair_face_set(Object *ob,
   for (int i = 0; i < totvert; i++) {
     if (fair_verts[i]) {
       interp_v3_v3v3(positions[i], orig_positions[i], positions[i], strength);
+      BKE_pbvh_vert_tag_update_normal(ss->pbvh, BKE_pbvh_index_to_vertex(ss->pbvh, i));
     }
   }
 }