try using the variable outside a string if that helps

Author: inariksit

.github/workflows/build-python-package.yml

@@ -49,6 +49,8 @@ jobs:
     - name: Build wheels on OSX
       if: startsWith(matrix.os, 'macos')
       env:
+        CFLAGS: "-arch ${{ matrix.macos_arch }}"
+        LDFLAGS: "-arch ${{ matrix.macos_arch }}"
         CIBW_BEFORE_BUILD: |
           cd src/runtime/c
           glibtoolize