act: Unrestricted set-env and add-path command processing enables environment injection

Summary act unconditionally processes the deprecated ::set-env:: and ::add-path:: workflow commands, which GitHub Actions disabled in October 2020 CVE-2020-15228, GHSA-mfwh-5m23-j46w due to environment injection risks. When a workflow step echoes untrusted data to stdout, an attacker can inject...