Make the tests pass with GCC from c8s

plan.fmf

@@ -14,5 +14,6 @@ discover:
     - gcc-c++
     test: |
       cd $(dirname $TMT_SOURCE_DIR/cffi-*/testing) &&
+      patch -p1 < $TMT_TREE/tests-no-error-sign-conversion.patch &&
       rm -rf cffi* &&
       pytest-3.12 testing/cffi0

python3.12-cffi.spec

@@ -11,6 +11,11 @@ License:        MIT and Python
 URL:            https://github.com/python-cffi/cffi
 Source:         %{url}/archive/v%{version}/cffi-%{version}.tar.gz
 
+# The GCC version in RHEL 8 errors with -Werror=sign-conversion due to
+#  https://github.com/python/cpython/issues/112353
+# This patch unconditionally adds -Wno-error=sign-conversion for tests
+Patch0:         tests-no-error-sign-conversion.patch
+
 BuildRequires:  python3-devel
 BuildRequires:  python3-pytest
 BuildRequires:  make

tests-no-error-sign-conversion.patch

@@ -0,0 +1,14 @@
+diff --git a/testing/support.py b/testing/support.py
+index 063e52c..24c6148 100644
+--- a/testing/support.py
++++ b/testing/support.py
+@@ -116,7 +116,8 @@ else:
+         # assume a standard gcc
+         extra_compile_args = ['-Werror', '-Wall', '-Wextra', '-Wconversion',
+                               '-Wno-unused-parameter',
+-                              '-Wno-unreachable-code']
++                              '-Wno-unreachable-code',
++                              '-Wno-error=sign-conversion']
+ 
+ is_musl = False
+ if sys.platform == 'linux':