Merge pull request #145 from MarkBaker/PHP8.1-Resolve-JsonSerializable-Return-Datatype-Deprecation

Php8.1 resolve json serializable return datatype deprecation

Author: mnapoli

src/Enum.php

@@ -311,6 +311,7 @@ public static function __callStatic($name, $arguments)
      * @link http://php.net/manual/en/jsonserializable.jsonserialize.php
      * @psalm-pure
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->getValue();