test: add regex check in test-buffer-bad-overload

Creating a buffer from a number should throw an error with a message
that describes the issue.

PR-URL: https://github.com/nodejs/node/pull/10038


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>