Update requirements.txt

[oxysoft]

Support latest version of torchaudio (already functional with no changes)

[oxysoft]

I had some problems using demucs in my project / cloud compute which uses torch 2.3.1, however I have updated all the libraries 2.3.1 and kept demucs and it's working just fine. Not all features have been tested, so keep that in mind

[CarlGao4]

Actually, the global backend selector has been completely removed since torchaudio 2.2. Users can't switch audio backend when separating, so the separation won't be affected using torchaudio 2.2+. However, training requires this feature or passing the desire audio backend would make the code mess. Besides, deciding how to specify the backend according to torchaudio version will make the logic even complex, so I think limiting torchaudio versions to below 2.2 is a good choice.