Currently there are a number of doctest failures when running sage with matplotlib 3.6, mostly deprecation warnings.

The current ticket is small and simple, it will make all tests pass with matplotlib 3.6, and it is backwards compatible.

Component: packages: standard

Author: Gonzalo Tornaría

Branch: 5501e0d

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34668