minor #17536 [Form] fix tests (xabbuh)

This PR was merged into the 2.7 branch.

Discussion
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[Form] fix tests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

e791fa0 [Form] fix tests

src/Symfony/Component/Form/Tests/Extension/Validator/Constraints/FormValidatorTest.php

@@ -135,6 +135,8 @@ class FormValidatorTest extends AbstractConstraintValidatorTest
         $form = new FormBuilder('name', '\stdClass', $this->dispatcher, $this->factory);
         $form = $form->setData($object)->getForm();
 
+        $this->expectValidateAt(0, 'data', $object, 'Default');
+
         $this->validator->validate($form, new Form());
 
         $this->assertNoViolation();