Tweak error message

Co-authored-by: Deepak Cherian <[email protected]>

Author: mgunyho

xarray/core/dataarray.py

@@ -591,8 +591,8 @@ def subset(dim, label):
             raise ValueError(
                 f"Splitting along the dimension {dim!r} would produce the variables "
                 f"{tuple(sorted(both_variables_and_coords))} which are also existing "
-                f"coordinates of the data. Use rename({rename_msg_fmt}) or "
-                f"assign_coords({dim}=...) to resolve this ambiguity."
+                f"coordinate variables. Use DataArray.rename({rename_msg_fmt}) or "
+                f"DataArray.assign_coords({dim}=...) to resolve this ambiguity."
             )
 
         indexes = filter_indexes_from_coords(self._indexes, coord_names)