It is documented that the input of __contains__ should be a real number, yet there is this doctest:

            sage: 'a' in A
            False

This will break after #22029.

Since this test is meaningless, it should just be removed.

CC: @JohnCremona

Component: coercion

Author: Jeroen Demeyer

Branch/Commit: 6a8b25b

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/26947