Update GraphAPIAdapter.php (#766)

v18.0 is going to be deprecated soon. Updating to v20.0 which has 2 years to deprecation (2026).

Author: cristiannancumeta

app/code/Meta/BusinessExtension/Helper/GraphAPIAdapter.php

@@ -55,7 +55,7 @@ class GraphAPIAdapter
     /**
      * @var string
      */
-    private $graphAPIVersion = 'v18.0';
+    private $graphAPIVersion = 'v20.0';
 
     /**
      * @var Client