Fix BC break for \Twig\Node\Expression\Test\DefinedTest in Twig 3.19

Problem/Motivation

https://github.com/twigphp/Twig/issues/4576

DefinedTest no longer accepts NameExpression so updating to 3.19 throws a syntax exception.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes