debian/control: depend on php-symfony-property-access

The upstream code uses the ObjectNormalizer class, and the Serializer
manual explicitly says that in this case the PropertyAccess component
must also be installed, see
https://symfony.com/doc/current/components/serializer.html#installation

Ensure that by depending explicitly on php-symfony-property-access, as
suggested in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824175