refactor: Resolve PHPStan issues from Rfc3339

Author: DannyvdSluijs

src/JsonSchema/Rfc3339.php

@@ -52,6 +52,7 @@ public static function createFromString($input): ?\DateTime
         if ($mutable === false) {
             throw new \RuntimeException('Unable to create DateTime from DateTimeImmutable');
         }
+
         $mutable->setTimezone($dateTime->getTimezone());
 
         return $mutable;