Instead of using libsass-python's `sass` module, which is incompatible
with Python 3.11, we now directly use libsass-python's `_sass` module,
which directly binds to the underlying C++ libsass library.
This ensures that the Sass build will not a blocker for the edx-platform
Python 3.11 upgrade, which needs to land in Redwood.
For more details, see the docstring at scripts/compile_sass.py#L167