fix(ci): suppress sign-conversion warnings on macOS

Apple Clang with -Werror treats RapidCheck library's sign-conversion
warnings as errors. Suppress these warnings on macOS since they come
from third-party dependencies, not our code.

Author: LessUp

.github/workflows/ci.yml

@@ -84,7 +84,7 @@ jobs:
         cmake -B build \
           -G Ninja \
           -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }} \
-          -DCMAKE_CXX_FLAGS="-march=native"
+          -DCMAKE_CXX_FLAGS="${{ matrix.os == 'macos-latest' && '-march=native -Wno-sign-conversion' || '-march=native' }}"
 
     - name: Build
       run: cmake --build build --config ${{ env.BUILD_TYPE }}