testing/py3-cstruct: disable on s390x

test_union_unpack test fails:

> tests/test_union.py:91: AssertionError
> =========================== short test summary info ============================
> FAILED tests/test_union.py::test_union_unpack - assert 7 == 187
> ========================= 1 failed, 77 passed in 0.34s =========================

testing/py3-cstruct/APKBUILD

@@ -5,7 +5,7 @@ pkgrel=0
 pkgdesc="C-style structs for Python"
 url="https://github.com/andreax79/python-cstruct"
 license="MIT"
-arch="noarch"
+arch="noarch !s390x" # test_union_unpack test fails on s390x
 makedepends="py3-gpep517 py3-setuptools py3-wheel"
 checkdepends="py3-pytest"
 subpackages="$pkgname-pyc"