Release internal/container

[roxblnfk]

Support PHP 8.1

• Add logic of readonly to an attribute in the container PHP 8.1 php-internal/container#4
• Use the attribute instead of readonly in the Testo code

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Package

• Create a repository
• Register in packagist https://packagist.org/packages/internal/container
• Replace the container in Testo
• Replace the container in buggregator/trap refactor: replace the in-tree DI container with internal/container buggregator/trap#218
• Replace the container in internal/dload refactor: replace the in-tree DI container with internal/container php-internal/dload#116

[roxblnfk]

Done