Add types to comply with symphony HTTPExceptionInterface

[bugzbrown]

issue

Error message when trying to use the user related endpoints:

Symfony\Component\ErrorHandler\Error\FatalError: Declaration of RLuders\JWTAuth\Exceptions\JsonValidationException::getStatusCode() must be compatible with Symfony\Component\HttpKernel\Exception\HttpExceptionInterface::getStatusCode(): int in /app/code/plugins/rluders/jwtauth/exceptions/JsonValidationException.php:12

fix

HTTPExceptionInterface in php 8> requires that the declaration contain types
This quick patch makes the JsonValidationException compatible to Symfony\Component\HttpKernel\Exception\HttpExceptionInterface again.

[rluders]

Thanks, @bugzbrown