Krikri::VariableSubstitutor::UnknownTestError
Raised for an unknown is <test> TEST name - the test-side sibling
of FilterEngine::UnknownFilterError. Real Jinja2/ansible-core
validates test names against the registered test set at template
COMPILE time and refuses the task with "No test named 'x'." (a
TemplateAssertionError, verified against ansible-core 2.19 via
sunfoxcz.dkim's own dkim_domains is not list - there is a list
FILTER and an is iterable test, but no is list TEST).