[codex] fix disabled beta release workflow

[ScriptedAlchemy]

Summary

Fixes the disabled beta release workflow so pushes to master no longer produce an invalid zero-job workflow failure.

Root Cause

release-beta.yml used the top-level env context inside job-level if expressions. GitHub does not allow env in job-level conditions, so the workflow failed before creating any jobs.

Changes

• Replace the invalid env.BETA_CHANNEL_ENABLED job guards with a repository-variable guard using vars.BETA_CHANNEL_ENABLED.
• Keep beta disabled unless the repository variable is set to true and the release trigger is restored.
• Update the workflow comment so the re-enable path is clear.

Validation

• Ran actionlint .github/workflows/*.yml.
• Parsed all workflow YAML files with PyYAML.
• Parsed release-plz.toml with tomllib.
• Ran git diff --check.

[changeset-bot]

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Latest commit: 5648fca

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