Add use_nested to internalAddGeneratedFile for php implementation (#6117)

diff --git a/php/src/Google/Protobuf/Internal/DescriptorPool.php b/php/src/Google/Protobuf/Internal/DescriptorPool.php
index 9b4dcc0..419bbf4 100644
--- a/php/src/Google/Protobuf/Internal/DescriptorPool.php
+++ b/php/src/Google/Protobuf/Internal/DescriptorPool.php
@@ -55,7 +55,7 @@
         return self::$pool;
     }
 
-    public function internalAddGeneratedFile($data)
+    public function internalAddGeneratedFile($data, $use_nested = false)
     {
         $files = new FileDescriptorSet();
         $files->mergeFromString($data);