E0282 suggests changing desugared loop variable to __next

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fn main() {
    for (ref i,) in [].iter() {
        i.clone();
    }
}

error[E0282]: type annotations needed
  --> $DIR/issue-20261.rs:14:11
   |
LL |     for (ref i,) in [].iter() {
   |         -------- consider giving `__next` a type
LL |         i.clone();
   |           ^^^^^ cannot infer type for `_`
   |
= note: type must be known at this point

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Duplicate of #51116.