resolve: Avoid some unstable iteration 2

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1036,7 +1036,7 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                                     Applicability::MaybeIncorrect,
                                 );
                                 // Do not lint against unused label when we suggest them.
-                                self.diag_metadata.unused_labels.remove(node_id);
+                                self.diag_metadata.unused_labels.swap_remove(node_id);
                             }
                         }
                     }