chore(CI): Re-run `pnpm install` after `pnpm build` in `build_reusable.yml` (#78720)
Apparently there's a chicken-and-egg problem between `pnpm install` and `pnpm build` where some packages depend on `pnpm build` being run first, but `pnpm build` can't run until after `pnpm install`.
Remove this one-off hack in `afterBuild` for `devlow-bench` and document it in `build_reusable.yml`.