error when decorating class with `@keyword` if the class contains an attribute with a type annotation

```py
from pytest_robotframework import keyword


@keyword
class Foo:
    asdf: int = 1
```

```
[ ERROR ] Error in library 'foo': Adding keyword 'Foo' failed: Type information given to non-existing argument 'asdf'.
```

i don't think (or care whether) `.robot` files support classes decorated with `@keyword`, but it works when called from python code so it should be allowed