[RFC] dropping CUDA 11.8 support in CI/CD

[atalman]

Related to: #145544

Opening this RFC to discuss dropping of CUDA 11.8 possibility and timeline

For PyTorch Release 2.7 we are proceeding with following configuration:
CUDA 11.8, CUDNN 9.1.0.70 - Same as Previous Release 2.6. No changes to CUDA 11.8 - Legacy version
CUDA 12.6 CUDNN 9.x - Version Released to Pypi - Stable version
CUDA 12.8 CUDNN 9.x - New Experimental version

Proposal is to drop it for release 2.8. Hence dropping support of 11.8 in nightlies for Mar 2025-Jun 2025.

cc @malfet @seemethere @ptrblck @msaroufim @eqy @tinglvv @nWEIdia

Versions

2.7-2.8

[zpcore]

Hi @miladm , @ysiraichi , CUDA 11.8 is already legacy status. I think we can drop 11.8 for PyTorch/XLA 2.7 release then.