Current behavior:

sage: G = DiGraph({0: ['a']})
sage: G.incidence_matrix()
Traceback (most recent call last)
...
TypeError: '<' not supported between instances of 'int' and 'str'

incidence_matrix method should be able to handle the case when vertices are of mismatched types.

Depends on #22349

CC: @dcoudert

Component: graph theory

Issue created by migration from https://trac.sagemath.org/ticket/29277