Reinstate some delayed bugs.

These were changed to `has_errors` assertions in #121071 because that
seemed reasonable, but evidently not.

Fixes #121103.
Fixes #121108.

compiler/rustc_ast_lowering/src/expr.rs

@@ -323,7 +323,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     )
                 }
                 ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
-                ExprKind::Err => hir::ExprKind::Err(self.dcx().has_errors().unwrap()),
+                ExprKind::Err => {
+                    hir::ExprKind::Err(self.dcx().span_delayed_bug(e.span, "lowered ExprKind::Err"))
+                }
                 ExprKind::Try(sub_expr) => self.lower_expr_try(e.span, sub_expr),
 
                 ExprKind::Paren(_) | ExprKind::ForLoop { .. } => {