Fix php8.1 deprecation error

[asika32764]

[asika32764]

The error was caused by https://github.com/WyriHaximus/reactphp-child-process-messenger/blob/master/src/ChildInterface.php#L11

Must change return type to mixed

[WyriHaximus]

This might not be invalid after all, does the error you mention at https://github.com/WyriHaximus/reactphp-child-process-messenger/pull/79#issue-839954256 disappear when you add this line?

[asika32764]

#[\ReturnTypeWillChange] won't work, must remove void from the interface return type.

[WyriHaximus]

#[\ReturnTypeWillChange] won't work, must remove void from the interface return type.

It is not there for the latest tagged version: https://github.com/WyriHaximus/reactphp-child-process-messenger/blob/4.0.2/src/ChildInterface.php#L16

[asika32764]

Close since the root library updated.