[stable29] use php-scoper

[backportbot[bot]]

Backport of #360

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• [ ] Review and resolve any conflicts

• [ ] Amend HEAD commit to remove the line stating to skip CI

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.