auto-approve.yml label actor

Trap: treating the sentry-internal-app[bot] accepted-label actor as the trusted opener looks reasonable because the Internal App has label permission, but GitHub records the app—not getsantry[bot] or sentry-release-bot[bot]—and app access proves no allowlisted request path. Fix: auto-approve.yml posts a github-actions[bot] request-bound proof before the Internal App adds accepted; authorize-approval.js accepts that label only when the proof matches the live request and allowlisted opener. Test the negative boundary: an Internal App label without its matching proof must be rejected.