tools: only use 2 cores for macos action

There are only 2 cores available so we shouldn't be using -j8

Refs: https://docs.github.com/en/free-pro-team@latest/actions/reference/specifications-for-github-hosted-runners#supported-runners-and-hardware-resources

PR-URL: https://github.com/nodejs/node/pull/36169


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Mary Marchini <oss@mmarchini.me>