MC-39901: Stabilize Web-API tests

- Fix phpstan issues

Author: eliseacornejo

dev/tests/api-functional/framework/Magento/TestFramework/TestCase/WebapiAbstract.php

@@ -258,10 +258,10 @@ public static function getFixture($key)
      *
      * @param \Magento\Framework\Model\AbstractModel $model
      * @param bool $secure
-     * @return \Magento\TestFramework\TestCase\WebapiAbstract
+     * @return void
      * //phpcs:disable
      */
-    public static function callModelDelete($model, $secure = false)
+    public static function callModelDelete($model, $secure = false) : void
     {
         //phpcs:enable
         if ($model instanceof \Magento\Framework\Model\AbstractModel && $model->getId()) {

dev/tests/api-functional/testsuite/Magento/Customer/Api/GroupRepositoryTest.php

@@ -40,7 +40,7 @@ class GroupRepositoryTest extends WebapiAbstract
     private $groupRepository;
 
     /**
-     * @var \Magento\Customer\Api\Data\groupInterfaceFactory
+     * @var \Magento\Customer\Api\Data\GroupInterfaceFactory
      */
     private $customerGroupFactory;