Read `torch-xpu-ops` pin directly from PyTorch

[whitneywhtsang]

When updating pytorch pin, e.g, #5609, .github/pins/e2e_reference_torch-xpu-ops.txt needs to be manually updated to match https://github.com/pytorch/pytorch/blob/365a6c84db516f244b7234b7aa3c8843af52936b/third_party/xpu.txt.

This issue is to allow reading the pin from third_party/xpu.txt directly, to eliminate this manual change.