style: use null coalescing assignment in getRequestData()

Rector's IfToNullCoalescingAssignRector flags the if-null block.

Author: rahul05ranjan

system/Superglobals.php

@@ -403,9 +403,7 @@ public function setRequestArray(array $array): self
      */
     public function getRequestData(?string $requestOrder = null): array
     {
-        if ($requestOrder === null) {
-            $requestOrder = ini_get('request_order');
-        }
+        $requestOrder ??= ini_get('request_order');
 
         if ($requestOrder === false || $requestOrder === '') {
             $requestOrder = ini_get('variables_order');