Update signature for php 8.4

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https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated

Deprecated: Onoi\CallbackContainer\CallbackContainerBuilder::__construct(): Implicitly marking parameter $callbackContainer as nullable is deprecated, the explicit nullable type must be used instead in …/vendor/onoi/callback-container/src/CallbackContainerBuilder.php on line 53