Function filter_attrs_for_multiple_eii_attr 

fn filter_attrs_for_multiple_eii_attr(
    ecx: &mut ExtCtxt<'_>,
    attrs: ThinVec<Attribute>,
    eii_attr_span: Span,
    eii_attr_path: &Path,
) -> ThinVec<Attribute>

Ensure that in the list of attrs, there’s only a single eii attribute.