Merge pull request #576 from saschagrunert/build-err-go1.23

Fix build error on go1.23rc1

Author: lthibault

list.go

@@ -1081,10 +1081,10 @@ func (s StructList[T]) Set(i int, v T) error {
 // A list of some Cap'n Proto capability type T.
 type CapList[T ~ClientKind] PointerList
 
-func (c CapList[T]) At(i int) (T, error) {
+func (c CapList[T]) At(i int) (res T, err error) {
 	ptr, err := PointerList(c).At(i)
 	if err != nil {
-		return T{}, err
+		return res, err
 	}
 	return T(ptr.Interface().Client()), nil
 }