test: copy addons .gitignore to test/abort/

`cp test/addons/.gitignore test/abort/.gitignore`, because the new
addon test in there leaves a build/ folder lying around and somebody
is bound to use `git add .` earlier or later.

Refs: https://github.com/nodejs/node/pull/31740

PR-URL: https://github.com/nodejs/node/pull/32624


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>