test: fix test data

$cleanValidationRules removes rules for missing keys.

Author: kenjis

tests/system/Models/ValidationModelTest.php

@@ -469,7 +469,7 @@ public function testInsertEntityValidateEntireRules()
         $entity = new SimpleEntity();
         $entity->setAttributes([
             'field1' => 'value1',
-            'field2' => '',
+            // field2 is missing
             'field3' => '',
             'field4' => '',
         ]);