Fix proper escaping by adding regex delimiter as the second argument

Problem/Motivation

• Fix proper escaping by adding regex delimiter as the second argument
  https://git.drupalcode.org/project/cloud/-/blob/4.x/modules/cloud_servic...

BEFORE:

$regex = '/\.(' . preg_replace('/ +/', '|', preg_quote($extensions)) . ')$/i';

AFTER:

$regex = '/\.(' . preg_replace('/ +/', '|', preg_quote($extensions, NULL)) . ')$/i';