MDL-77337 analytics: 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.

analytics/classes/action.php

@@ -70,6 +70,9 @@ abstract class action {
      */
     protected $text = null;
 
+    /** @var string Store the action type. */
+    protected string $type = '';
+
     /**
      * Returns the action name.
      *