Deprecated warnings with PHP 8

[matbech]

Deprecated: Required parameter $path follows optional parameter $schema in justinrainbow/json-schema/src/JsonSchema/Constraints/UndefinedConstraint.php on line 62
PHP Deprecated: Required parameter $path follows optional parameter $schema in justinrainbow/json-schema/src/JsonSchema/Constraints/UndefinedConstraint.php on line 108

[erayd]

Thanks - please feel free to submit a PR fixing this.

[erayd]

Fixed by @matbech in #619.