scoper-autoload.php doesn't support PHP 5.6 (again)

[marekdedic]

Bug report

Question	Answer
PHP-Scoper version	0.18.7
PHP version	5.6
Platform with version	all
Github Repo	-

This is a followup to #842. I found another thing in scoper-autoload.php that is incompatible with PHP 5.6 - the ?? operator. PR incoming.

See the error here: https://github.com/skaut/skaut-google-drive-gallery/actions/runs/8883783876/job/24391429247?pr=2632