tools: skip macOS GitHub Actions test on doc-only changes

We skip macOS GitHub Actions pushes on doc-only changes but the
intention was no doubt to skip them on pull requests too. We still run
the tests on Linux, so addons tests will still run when addons docs
change.

PR-URL: https://github.com/nodejs/node/pull/38296


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>