fix test_histogram_loss

[GaetanLepage]

With pytorch 2.1.0, the following test fail:

tests/losses/test_histogram_loss.py::TestHistogramLoss::test_histogram_loss

Log:

         if self.cuda:
             histogram_pos_inds = histogram_pos_inds.cuda()
>       histogram_pos_repeat[histogram_pos_inds] = 0
E       RuntimeError: masked_fill_ only supports boolean masks, but got mask with dtype unsigned char

tests/losses/test_histogram_loss.py:112: RuntimeError

This patch should address it.

[KevinMusgrave]

Thanks @GaetanLepage !