Pin py-torch to 1.9.1

(due to a known build fail of 1.10.x → to be investigated later)

It seems that we would have to enable the tensorpipe feature for version 1.10.x to build (cf. https://github.com/pytorch/pytorch/issues/68002)… however, I'd like to have a "minimal" pytorch first .

merged

mentioned in commit 7a2adf01

Hi @emuller,

This has been successfully built. Let me know if we need to do something more.