build: do not run auto-start-ci on forks

Previously, the auto-start-ci action would run on forks.
Without the secrets, the action would fail over and over again.
This caused a lot of email spam. Now, we only run this action
when the repository is nodejs/node.

PR-URL: https://github.com/nodejs/node/pull/34650


Reviewed-By: Mary Marchini <oss@mmarchini.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>