Update src/magpylib_material_response/demag.py

Co-authored-by: Copilot <[email protected]>

Author: Alexboiboi

src/magpylib_material_response/demag.py

@@ -66,7 +66,7 @@ def _convert_to_array(susceptibility, n):
     if (
         hasattr(susceptibility, "__len__")
         and len(susceptibility) == 3
-        and not isinstance(susceptibility[0], list | tuple | np.ndarray)
+        and all(not isinstance(x, (list, tuple, np.ndarray)) for x in susceptibility)
     ):
         # This is a 3-vector, not a list of 3 items
         susis = np.tile(susceptibility, (n, 1))