MDL-77350 badges: Added class properties that are not declared

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

badges/classes/backpack_api_mapping.php

@@ -79,6 +79,12 @@ class backpack_api_mapping {
     /** @var string Error string from authentication request. */
     private static $authenticationerror = '';
 
+    /** @var mixed List of parameters for this method. */
+    protected $postparams;
+
+    /** @var int OpenBadges version 1 or 2. */
+    protected $backpackapiversion;
+
     /**
      * Create a mapping.
      *