[llama-mm] Bump PyTorch pin to 11/12 (#6819)

Summary: As titled.

Test Plan: Rely on CI jobs.

Reviewers:

Subscribers:

Tasks:

Tags:

ghstack-source-id: 85c2c56c23ed6edf008c8a287a287bb3747e71a9
Pull Request resolved: https://github.com/pytorch/executorch/pull/6805

Co-authored-by: Mengwei Liu <larryliu@meta.com>