Linter doesn't catch invalid template test

[miketheman]

From #13457

Raised a TemplateError for if foo is None

Why doesn't curlylint catch this?

[miketheman]

During investigation, I learned that the test here doesn't actually render templates - rather the get_template() method calls the filesystem and loads the file only, doesn't actually render it (we'd need to inject piles of variables for that to happen).

This test will catch a class of errors like missing endif tags (jinja2.exceptions.TemplateSyntaxError), but doesn't perform the testing that would have surfaced an invalid test condition (aka jinja2.exceptions.TemplateRuntimeError)

[miketheman]

I opened thibaudcolas/curlylint#153 to discuss this kind of thing.

[miketheman]

Also test this against djlint