for_loop_over_fallibles: fix suggestion for "remove .next()" case

if the iterator is used after the loop, we need to use `.by_ref()`

compiler/rustc_lint/src/for_loop_over_fallibles.rs

@@ -82,7 +82,7 @@ impl<'tcx> LateLintPass<'tcx> for ForLoopOverFallibles {
                 warn.span_suggestion(
                     recv.span.between(arg.span.shrink_to_hi()),
                     format!("to iterate over `{recv_snip}` remove the call to `next`"),
-                    "",
+                    ".by_ref()",
                     Applicability::MaybeIncorrect
                 );
             } else {

src/test/ui/lint/for_loop_over_fallibles.stderr

@@ -37,9 +37,8 @@ LL |     for _ in [0; 0].iter().next() {}
    |
 help: to iterate over `[0; 0].iter()` remove the call to `next`
    |
-LL -     for _ in [0; 0].iter().next() {}
-LL +     for _ in [0; 0].iter() {}
-   |
+LL |     for _ in [0; 0].iter().by_ref() {}
+   |                           ~~~~~~~~~
 help: consider using `if let` to clear intent
    |
 LL |     if let Some(_) = [0; 0].iter().next() {}