Fix unsafe caching for isolated tests (#45602)
Noticed while testing across CI environments that the `test-pack` handling is not-concurrent or cache safe so this removes it from being used by default and moves it behind a flag to allow further investigating later.
In CI if `test-pack` is called at the same time due to multiple concurrency it can cause the resulted archive to be corrupted so may require a form of lock to resolve in CI although locally re-using the same archive name/path isn't safe with pnpm as it won't bust the store cache and continue to leverage previous cache.
