fix(stubs): mark parameters as explicitly nullable

Author: msbit

stubs/stream_socket_client.stub

@@ -1,8 +1,8 @@
 <?php
 
 /**
- * @param-out int $error_code
- * @param-out string $error_message
+ * @param-out int|null $error_code
+ * @param-out string|null $error_message
  * @param resource|null $context
  * @return resource|false
  */

stubs/stream_socket_server.stub

@@ -1,8 +1,8 @@
 <?php
 
 /**
- * @param-out int $error_code
- * @param-out string $error_message
+ * @param-out int|null $error_code
+ * @param-out string|null $error_message
  * @param resource|null $context
  * @return resource|false
  */