fix: allow prereleases from main candidates

[Obed0101]

Problem

The beta16 release workflow failed before publishing because prerelease candidates from main were required to be ancestors of origin/dev. The promoted main commit is intentionally not an ancestor of dev after the squash promotion.

Solution

Allow a prerelease source SHA to be verified against either origin/dev or origin/main, while preserving the stable-release requirement that candidates come from main.

Verification

• git diff --check — passed.
• Local ancestry check — confirmed the current main candidate is an ancestor of origin/main and not of origin/dev.
• Release run 35916028675 — confirmed the prior failure was exactly this guard.

Scope

One line in .github/workflows/release.yml; no product/runtime behavior changes.

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