v2.8.11-canary.15

<!-- Release notes generated using configuration in .github/release.yml at v2.8.11-canary.15 -->

What's Changed

Changelog

• perf: Replace git subprocesses with libgit2 and skip unnecessary summary work by @anthonyshew in https://github.com/vercel/turborepo/pull/11938

Full Changelog: https://github.com/vercel/turborepo/compare/v2.8.11-canary.14...v2.8.11-canary.15