CI: warnings when building macOS binaries on GA

The build process on GitHub Actions (GA) is warning about versions:

> Warning: This wheel needs a higher macOS version than the version your Python interpreter is compiled against. To silence this warning, set MACOSX_DEPLOYMENT_TARGET to at least 10_13 or recreate these files with lower MACOSX_DEPLOYMENT_TARGET:
> Warning: st.macosx-10.9-universal2/wheel/dss_python_backend/libklusolvex.dylib[WARNING] This wheel needs a higher macOS version than the version your Python interpreter is compiled against. To silence this warning, set MACOSX_DEPLOYMENT_TARGET to at least 10_13 or recreate these files with lower MACOSX_DEPLOYMENT_TARGET:

Since the lowest supported version on GA is 11, if someone has issues in actual usage, please let us know here.