Merge branch '3.4' into 4.4

* 3.4:
  Revert "[travis][appveyor] don't cache .phpunit"
  silence E_NOTICE triggered since PHP 7.4
  [Form] Removed legacy check in `ValidationListener`
  do not merge constraints within interfaces
  [Validator] Fixed default group for nested composite constraints

Author: nicolas-grekas

Extension/Validator/EventListener/ValidationListener.php

@@ -50,8 +50,7 @@ public function validateForm(FormEvent $event)
             foreach ($this->validator->validate($form) as $violation) {
                 // Allow the "invalid" constraint to be put onto
                 // non-synchronized forms
-                // ConstraintViolation::getConstraint() must not expect to provide a constraint as long as Symfony\Component\Validator\ExecutionContext exists (before 3.0)
-                $allowNonSynchronized = (null === $violation->getConstraint() || $violation->getConstraint() instanceof Form) && Form::NOT_SYNCHRONIZED_ERROR === $violation->getCode();
+                $allowNonSynchronized = $violation->getConstraint() instanceof Form && Form::NOT_SYNCHRONIZED_ERROR === $violation->getCode();
 
                 $this->violationMapper->mapViolation($violation, $form, $allowNonSynchronized);
             }