Bug in the generalized Wasserstein Dice loss

[LucasFidon]

Describe the bug The values returned by the loss are not correct for batch sizes larger than 1

To Reproduce In the binary case and for M=[[1,0],[0,1]] the generalized Wasserstein Dice loss should be the same as the Dice loss. For batch size > 1 it is not the case.

Expected behavior See above. For this special case the GWDL and the DL should return the same values.

Additional context I am the author of the generalized Wasserstein Dice loss paper and the bug has been already fixed in my git repository https://github.com/LucasFidon/GeneralizedWassersteinDiceLoss I will fix the bug in MONAI too and add unit tests.