[CI] Support dev releases and un-hardcode package index URL in full PyTorch test dispatch

[ethanwee1]

Context

Follow-up from #4499 review (ScottTodd). The full PyTorch test dispatch in multi_arch_release_linux_pytorch_wheels.yml currently:

• Only dispatches for release_type == 'nightly', so dev releases are not tested.
• Hardcodes PACKAGE_INDEX_URL: "https://rocm.nightlies.amd.com/whl-multi-arch/" in the dispatch job env.

Ask

• Support dispatching full tests for dev releases (not only nightly).
• Un-hardcode the package index URL so it is derived from the release type / build outputs instead of a literal nightly URL.

Notes

Related follow-ups: #5777 (per-ref build status), #5755 (generalize beyond Linux gfx942), #5110 (manifests).