test: update the canal number wrt the way neigbors are now ordered

so that it matches the fig51

test/bfs-spanning-tree/fig51.dot

 graph fig4_1 {
  graph [k=42]
 
- p1 [algo="root.ml" init="d=2 par=0"]
- p2 [algo="p.ml"    init="d=0 par=0"]
- p3 [algo="p.ml"    init="d=2 par=0"]
- p4 [algo="p.ml"    init="d=4 par=1"]
- p5 [algo="p.ml"    init="d=3 par=1"]
- p6 [algo="p.ml"    init="d=4 par=1"]
- p7 [algo="p.ml"    init="d=1 par=2"]
+ p1 [algo="root.ml" init="d=2 par=-1"]
+ p2 [algo="p.ml"    init="d=0 par=1"]
+ p3 [algo="p.ml"    init="d=2 par=2"]
+ p4 [algo="p.ml"    init="d=4 par=0"]
+ p5 [algo="p.ml"    init="d=3 par=0"]
+ p6 [algo="p.ml"    init="d=4 par=0"]
+ p7 [algo="p.ml"    init="d=1 par=1"]
  p8 [algo="p.ml"    init="d=3 par=0"]
 
  p1 -- p2 -- p3 -- p4 -- p5 -- p6 -- p7 -- p8 -- p1