symfony/flex contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe. You can run "composer config --no-plugins allow-plugins.symfony/flex [true|false]" to enable it (true) or disable it explicitly and suppress this exception (false) See https://getcomposer.org/allow-plugins

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The following actions uses node12 which is deprecated and will be forced to run on node16: actions/checkout@v2, actions/cache@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/