MAGETWO-90998: Extension developer has to specify all fields in order to extend content type.

- fix testStrictTypes failure

Author: krissyhiserote

dev/tests/integration/testsuite/Magento/PageBuilder/_files/content_type/groups_expected_merged_array.php

@@ -3,6 +3,9 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+
+declare(strict_types=1);
+
 return [
     'groups' => [
         'group1' => [

dev/tests/integration/testsuite/Magento/PageBuilder/_files/content_type/type3_expected_merged_array.php

@@ -3,6 +3,9 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+
+declare(strict_types=1);
+
 return [
     'types' => [
         'type3' => [