Test using illegal Modelica code not expecting error

[AnHeuermann]

Some of the tests inside test/corpus are using illegal Modelica code but are expecting an error free tree as output.

E.g. in https://github.com/OpenModelica/tree-sitter-modelica/blob/master/test/corpus/a2-2_der_enum_extend_classes.txt#L5-L18

model foo = der(bar, foo);

is wrong in every aspect. I'm not even sure what this should be.