Fix label binarize for binary class

[jinsolp]

Closes #5740

Fix for cuml's label_binarize to have the same output as scikit-learn's label_binarize for binary classes.

Note: Unlike scikit-learn's scipy.sparse._csr.csr_matrix.getcol(), cuml's cupyx.scipy.sparse.csr_matrix.getcol() does not support -1 indexing.

[beckernick]

Note: Unlike scikit-learn's scipy.sparse._csr.csr_matrix.getcol(), cuml's cupyx.scipy.sparse.csr_matrix.getcol() does not support -1 indexing.

Can you file a feature request for this on CuPy (if there isn't on already)? Feels like this is probably a small tweak to existing slicing logic.

[jinsolp]

I don't think they have it already.
I made an issue here.

[divyegala]

/merge