Refactor Json::isJson() to use json_validate function

Now that we've dropped support for PHP 8.2, we can use PHP's json_validate function.

Author: duncanmcclean

src/Support/Json.php

@@ -15,7 +15,6 @@ public static function isJson($value): bool
             return false;
         }
 
-        // TODO: Replace this with json_validate when dropping support for PHP 8.2.
-        return is_array(json_decode($value, true));
+        return json_validate($value);
     }
 }