Thin wrapper around pytest for running it in the Sage environment.

as suggested in #31924 comment:94

Similar to our existing wrapper sage -tox.

CC: @tornaria @tobiasdiez @soehms

Component: doctest framework

Author: Matthias Koeppe

Branch/Commit: 8825079

Reviewer: Tobias Diez

Issue created by migration from https://trac.sagemath.org/ticket/33572