Trac #28531: bliss canonical labels ignores edge labels

We consider below a path of 3 vertices. The two edges carry different
labels. In particular it has no automorphism. Below bliss simply ignores
the edge labels
{{{

sage: for algo in ['sage', 'bliss']:
....:     G = Graph([(0,1,2),(0,2,1)])
....:     H = Graph([(0,1,1),(1,2,2)])
....:     Gcan, Gmap = G.canonical_label(edge_labels=True,
certificate=True, algorithm=algo)
....:     Hcan, Hmap = H.canonical_label(edge_labels=True,
certificate=True, algorithm=algo)
....:     print(sorted(Gcan.edges()) == sorted(Hcan.edges()))
True
False
}}}
(note: instead of comparing the sorted list of edges, one can
alternatively set `weighted=True` in the constructors)

URL: https://trac.sagemath.org/28531
Reported by: vdelecroix
Ticket author(s): Vincent Delecroix
Reviewer(s): David coudert

Author: Release Manager