macos_pyside_min_deployment_target incorrectly assumes get_config_var always returns a string

The helper function macos_pyside_min_deployment_target in{{ build_scripts/wheel_utils.py}} incorrectly assumes that get_config_var('MACOSX_DEPLOYMENT_TARGET') always returns a string or None. This is not the case on MacOS Big Sur where the SDK version is returned as an integer when using SDK version 11. This results in an exception when the version is split into major and minor parts and prevents a successful build.

I have been able to work around the issue by modifying the line that splits the version number (note the explicit string conversion):

python_target_split = [int(x) for x in str(python_target).split('.')]