`Schematic\Entry::jsonSerialize()` should be compatible with `JsonSerializable::jsonSerialize(): mixed`

[trejjam]

Hi,
I am using your library in my own library. I run tests also against PHP8.1. I have an issue with an override of Schematic\Entry::jsonSerialize() as you can see here: https://github.com/trejjam/mailchimp/runs/7054121857#step:11:25

What is a solution which will suit you? Update signature, or define #[\ReturnTypeWillChange] ignoring attribute?