release(turborepo): 2.9.15-canary.8 (#12945)
## Why
The 2.9.15-canary.8 release workflow failed during npm provenance after
partially publishing packages. We are not recovering that canary
publish, but main still needs the generated release metadata bump so
future canaries move forward.
## What
Updates generated release metadata from 2.9.15-canary.7 to
2.9.15-canary.8. No code changes, release tag, or publish retry.
## How
Generated from failed release run SHA 31123f47 with `scripts/version.js
prerelease` and `cli make prepare-stage-release`. Pre-push hooks passed:
`lint-staged`, `turbo run format check:toml`, `cargo fmt --check`,
`cargo lint`, and `cargo check --workspace`.
