26306594 Restored CI `perf-tests` job for boot time benchmarking
ref https://github.com/TryGhost/Ghost/pull/26512
- `job_perf-tests` was removed in #26512 (2026-02-19) because
`TryGhost/Ghost-Benchmarks` had been archived, so the push step failed
on every main merge that touched core
- that repo was unarchived on `2026-07-19`, so the original blocker is gone
- the measurement is a faithful restore: same hyperfine version (1.18.0),
same invocation, same jq transform, same destination, so the existing
3,757-point series continues rather than restarting
- the surrounding plumbing had to change: `./.github/actions/restore-cache`
no longer exists (replaced by `pnpm install`), `yarn` became `pnpm`, and all
actions are now SHA-pinned per org policy
- not added to `job_required_tests` - this charts a trend, it doesn't gate
merges (at the moment)