fix rebase error

Author: tiif

compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs

@@ -31,6 +31,7 @@ impl<S: Stage> CombineAttributeParser<S> for UnstableFeatureBoundParser {
     const PATH: &'static [rustc_span::Symbol] = &[sym::unstable_feature_bound];
     type Item = (Symbol, Span);
     const CONVERT: ConvertFn<Self::Item> = AttributeKind::UnstableFeatureBound;
+    const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,