Duplicate PTY shutdown signals fixed

<!-- Release notes generated using configuration in .github/release.yml at v2.9.19-canary.7 -->

What's Changed

Changelog

• release(turborepo): 2.9.19-canary.6 by @github-actions[bot] in https://github.com/vercel/turborepo/pull/13092
• fix: Prevent duplicate PTY graceful shutdown signals by @anthonyshew in https://github.com/vercel/turborepo/pull/13093

Full Changelog: https://github.com/vercel/turborepo/compare/v2.9.19-canary.6...v2.9.19-canary.7