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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Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v2. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.