test: reduce scope of variable in common module

arrayBufferViews is used by only one function so scope it to that
function (in the common module).

PR-URL: https://github.com/nodejs/node/pull/17830


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>