ScaffoldUpgradeTest and ScaffoldTest rely on packagist.org

Problem/Motivation

\Drupal\Tests\Composer\Plugin\Scaffold\Functional\ScaffoldUpgradeTest and \Drupal\Tests\Composer\Plugin\Scaffold\Functional\ScaffoldTest failed today:

• 9.1.x https://www.drupal.org/pift-ci-job/1717803
• 9.0.x https://www.drupal.org/pift-ci-job/1717806

I've attached the phpunit xml output from the tests. It looks like this tests need the internet.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet