Symfony version(s) affected: 4.4.0

Description
In Symfony 4.3.4 Symfony\Component\Validator\ConstraintViolationInterface::getMessage() returns string.
In Symfony 4.4.0 it returns string|object.

Widening return types is a BC break that breaks contract for consumers.

Caught by PHPStan:

Parameter #1 $message of class InvalidArgumentException constructor expects string, object|string given.