Issue #3570436: Normalize composer.json repositories as lists in expand_composer_json.php

Leszek Masłowskirequested to merge
issue/gitlab_templates-3570436:3570436-composer29-compat into main

Fixes Composer 2.9 validation errors related to expanded repositories. See https://www.drupal.org/project/gitlab_templates/issues/3570436

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