ConvexSet_base, Polyhedron_base: In _test methods, do not fail if some modules are unavailable

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(cherry-picked from #32432)


CC:  @kliem

Component: **refactoring**

Author: **Matthias Koeppe**

Branch/Commit: **[`52ac1da`](https://github.com/sagemath/sagetrac-mirror/commit/52ac1dac69cfc8b869459e08408ff94ff2f81611)**

Reviewer: **Jonathan Kliem**

_Issue created by migration from https://trac.sagemath.org/ticket/32628_

