[BUG] cudf.DataFrame.ewm.mean returns TypeError: Implicit conversion to a host NumPy array via __array__ is not allowed

[Matt711]

Describe the bug
cudf.DataFrameewm.mean raises a TypeError

TypeError: Implicit conversion to a host NumPy array via __array__ is not allowed, To explicitly construct a GPU matrix, consider using .to_cupy()
To explicitly construct a host matrix, consider using .to_numpy().

Steps/Code to reproduce bug

In [1]: import cudf

In [2]: cdf=cudf.DataFrame(range(10))

In [3]: cdf.ewm(0.5).mean() # TypeError

Expected behavior
It should return the same result as Pandas.