refactor: add hemisphere and remove kwargs from call to geoid

src/polartoolkit/fetch.py

@@ -2137,7 +2137,7 @@ def preprocessing(fname: str, action: str, _pooch2: typing.Any) -> str:
                 spacing=initial_spacing,
                 region=initial_region,
                 registration=initial_registration,
-                **kwargs,
+                hemisphere="south",
             )
             # convert from ellipsoid back to eigen geoid
             grid = grid - eigen_correction