flash-attn2: no build variant for torch 2.13

[qgallouedec]

kernels-community/flash-attn2 ships variants for torch 2.7–2.12. With torch 2.13 installed, get_kernel fails:

Cannot find a build variant for this system in kernels-community/flash-attn2
torch212-cxx11-cu126-x86_64-linux: Torch version (2.12) does not match environment Torch version (2.13)

Could torch 2.13 builds be added?

Hit in TRL CI (huggingface/trl#6741), where attn_implementation="kernels-community/flash-attn2" tests are now xfailed.

[danieldk]

Version 3 has Torch Stable ABI build that work with any Torch version >= 2.9:

https://huggingface.co/kernels/kernels-community/flash-attn2/tree/v3/build

I am not sure if transformers already has some syntax for specifying a version in the attn_implementation string, but since versions are implemented as branches named v<version>, I think attn_implementation="kernels-community/flash-attn2@v3 should work.