.github/workflows/tox-gcc_spkg.yml: Disable tests on some platforms that fail --without-system-gcc #29815
Description
Until work is done on #29675, it is not necessary to repeatedly build on platforms that are known to fail.
Depends on #29757
Component: porting
Author: Matthias Koeppe
Branch/Commit: c02ea22
Reviewer: Jonathan Kliem
Issue created by migration from https://trac.sagemath.org/ticket/29815