Sage's noncommutative rings don't always increment a refcount #13145
Description
Running doctests with the new doctest framework revealed that KeyErrors were being ignored in sage.lib.singular.ring.singular_ring_delete.
Component: commutative algebra
Author: David Roe
Reviewer: Martin Albrecht
Merged: sage-5.4.beta1
Issue created by migration from https://trac.sagemath.org/ticket/13145