py3: Fix categories/regular_supercrystals.py for python3

[vklein]

• Sort result of Digraph.sinks().
• Fix regular_supercrystals.py doctests.
• In type_Q.py CartanType?.index_set, fix range usage as a list (it's an iterator in python3).

An unique doctest error is remaining but it should be fixed by #26267

[vklein]

New commits:

​629fe2d

Trac #26275 : Fix categories/regular_supercrystals.py ...

[tscrim]

+1 to the other changes but strong -1 to sorting the sinks(). The vertices (and hence the output) may not be sortable. The better thing to do in this case is to either directly call sorted on the offending doctests (which I don't really care for, but you cannot get around that for a non-deterministic doctest) or add a sort=False keyword to sinks(). Anyways, the changes to sinks() should be done on a separate ticket for better separations-of-concerns and matched with a corresponding change to sources and similar methods.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​71986e2

Trac #26275 : Revert Digraph.sink() modification ...

[vklein]

Changes to sinks() reverted. I sorted the doctest results instead.

[tscrim]

I get a doctest failure due to this change:

                 sage: T = B.tensor(B)
                 sage: T.lowest_weight_vectors()
-                ([3, 3], [3, 2])
+                ([3, 2], [3, 3])
 

Did you want a sorted on that output as well?

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​da30802

Trac #26275 : Revert Digraph.sink() modification ...

[vklein]

Apparently py2 test have not be done with ​71986e2. Sorry for that. da30802 fix the problem.

[tscrim]

Thank you.