Silence redundant warning when E0038 will be emitted

compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -122,6 +122,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ],
                     Applicability::MachineApplicable,
                 );
+            } else {
+                // We'll emit the object safety error already, with a structured suggestion.
+                diag.downgrade_to_delayed_bug();
             }
             return true;
         }
@@ -145,6 +148,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
             if !is_object_safe {
                 diag.note(format!("`{trait_name}` it is not object safe, so it can't be `dyn`"));
+                // We'll emit the object safety error already, with a structured suggestion.
+                diag.downgrade_to_delayed_bug();
             } else {
                 let sugg = if let hir::TyKind::TraitObject([_, _, ..], _, _) = self_ty.kind {
                     // There are more than one trait bound, we need surrounding parentheses.