build: spawn `make test-ci` with `-j1`

All the sub targets have internal parallelism, so no performance loss.
Also `make` doesn't to a good enough job of combining the output
streams, or eliminate races.

PR-URL: https://github.com/nodejs/node/pull/23733
Fixes: https://github.com/nodejs/node/issues/22006


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>