Pass release branches separately from pull request refs

In GitHub Actions, a pull_request run checks out a synthetic merge ref. A release selector that derives its target branch from GITHUB_REF can reject a valid PR even when a step's env block appears to override that name. Pass the target release branch through a separate explicit input, allowlist it, and compare the checked-out commit with the run SHA. Test the selector with a refs/pull/.../merge ref so branch-target logic is exercised before PR CI.

Applies when: The same release workflow validates pull requests and runs branch deployments. Keywords: GitHub Actions pull_request GITHUB_REF merge ref branch selector CI