minor #37855 [Validator] fix tests (xabbuh)

This PR was merged into the 3.4 branch.

Discussion
----------

[Validator] fix tests

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

Commits
-------

f04f507cd5 [Validator] fix tests

src/Symfony/Component/Validator/Test/ConstraintValidatorTestCase.php

@@ -115,7 +115,7 @@ abstract class ConstraintValidatorTestCase extends TestCase
         $validator->expects($this->any())
             ->method('inContext')
             ->with($context)
-            ->willReturn($this->createMock(AssertingContextualValidator::class));
+            ->willReturn($this->getMockBuilder(AssertingContextualValidator::class)->setMethods(null)->getMock());
 
         return $context;
     }