`torch.quantize_per_channel` triggers deprecation warning in torch 2.13

[andrea-fasoli]

Running CICD with torch 2.13 triggers deprecation warning, making the test suite fail and preventing bumping the torch version in #209 .

    E           UserWarning: torch.quantize_per_tensor, torch.quantize_per_channel and other quantized tensor creation functions that produce tensors with dtype torch.quint8, torch.qint8, and torch.qint32 are deprecated and will be removed in a future PyTorch release. Please see https://github.com/pytorch/pytorch/issues/184982 for more information. (Triggered internally at /__w/pytorch/pytorch/aten/src/ATen/quantized/Quantizer.cpp:111.)

This call can be replaced with equivalent plain arithmetic.