Add test_build_wheels_linux_v2.yml: build torchvision via uv-based v2

[atalman]

Summary

Adds test_build_wheels_linux_v2.yml — a CI test that builds torchvision (pytorch/vision) through the uv-based build_wheels_linux_v2.yml introduced in #8336.

⚠️ Depends on #8336

This test's uses: ./.github/workflows/build_wheels_linux_v2.yml won't resolve until #8336 (the v2 workflow) is on main, so CI here is expected to be red until #8336 merges. Kept as a clean, test-only diff intentionally — merge #8336 first, then this turns green.

Why torchvision

torchvision is a compiled C++/CUDA extension (setup-py + packaging/pre_build_script.sh/post_build_script.sh + test/smoke_test.py), so it exercises the full uv path end-to-end: uv-provisioned interpreter, cmake/ninja toolchain, torch-dep install, manylinux repair, and smoke test. A pure-python package wouldn't.

Notes

• Mirrors the existing test_build_wheels_linux_with_cuda.yml vision matrix (CUDA + ROCm + XPU + CPU) but builds vision only, targeting v2.
• If the manylinux builder images don't ship openssl/libpng/libwebp/pkg-config (previously conda-supplied), the vision build will surface it here — torchvision's pre_build_script.sh already installs several of its own system deps, so it's a good canary.
• Triggers on workflow_dispatch and PRs touching the v2 workflow / matrix / pkg-helpers.

[vercel]

@atalman is attempting to deploy a commit to the Meta Open Source Team on Vercel.

A member of the Team first needs to authorize it.

[atalman]

Superseded by #8336 — merged the v2 workflow and the torchvision test into a single PR (matrix trimmed to Python 3.12). Closing.