_sanitize_path fails on Python 3.12

[mpasternak]

Traceback

    def _sanitize_path(filepath):
        try:
            path_root = Path(getattr(settings, 'SENDFILE_ROOT', None))
        except TypeError:
            raise ImproperlyConfigured('You must specify a value for SENDFILE_ROOT')
    
        filepath_obj = Path(filepath)
    
        # get absolute path
        # Python 3.5: Path.resolve() has no `strict` kwarg, so use pathmod from an
        # already instantiated Path object
>       filepath_abs = Path(filepath_obj._flavour.pathmod.normpath(str(path_root / filepath_obj)))
E       AttributeError: module 'posixpath' has no attribute 'pathmod'

Fix

1. actions & readme needs updating so we start testing on 3.12
2. code (obviously!) needs updating

Who?

I don't have a PR ready yet, this is a simple fix but some time needs to be spent. Currently I'm not working on this, but if anything changes I'll let you know.

Thanks for maintaining django-sendfile!

[moggers87]

Fixed in #60