gh-36040: Fix failing doctest in sage/graphs/bliss.pyx
Since 10.1.beta9, a doctest is failing in `sage/graphs/bliss.pyx` due to
some changes in `sage/groups/perm_gps/permgroup.py`. One of them is that
method `.gens()` now returns a tuple and no longer a list.
```py
sage: # optional - bliss
sage: from sage.graphs.bliss import automorphism_group
sage: alpha = "abcdefghijklmnopqrstuvwxyz"
sage: G = Graph()
sage: G.add_edges((alpha[i],alpha[j],"A") for i in range(0, 2)
for j in range(14,20))
sage: G.add_edges((alpha[i],alpha[j],"B") for i in range(2, 5)
for j in range(14,20))
sage: G.add_edges((alpha[i],alpha[j],"C") for i in range(5, 9)
for j in range(14,20))
sage: G.add_edges((alpha[i],alpha[j],"D") for i in range(9,14)
for j in range(14,20))
sage: A = automorphism_group(G)
sage: print(A.gens())
```
```py
Failed example:
print(A.gens())
Expected:
[('r','t'), ('s','r'), ('p','s'), ('q','p'), ('o','q'), ('l','n'),
('m','l'), ('j','m'), ('k','j'), ('i','h'), ('f','i'), ('g','f'),
('e','d'), ('c','e'), ('a','b')]
Got:
(('m','n'), ('l','m'), ('k','l'), ('j','k'), ('h','i'), ('g','h'),
('f','g'), ('d','e'), ('c','d'), ('s','t'), ('r','s'), ('q','r'),
('p','q'), ('o','p'), ('a','b'))
```
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URL: https://github.com/sagemath/sage/pull/36040
Reported by: David Coudert
Reviewer(s): Frédéric Chapoton
