Rollup merge of #121109 - nnethercote:TyKind-Err-guar-2, r=oli-obk

Add an ErrorGuaranteed to ast::TyKind::Err (attempt 2)

This makes it more like `hir::TyKind::Err`, and avoids a `has_errors` assertion in `LoweringContext::lower_ty_direct`.

r? ```@oli-obk```

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1048,11 +1048,16 @@ impl<'a> State<'a> {
             ast::TyKind::Infer => {
                 self.word("_");
             }
-            ast::TyKind::Err => {
+            ast::TyKind::Err(_) => {
                 self.popen();
                 self.word("/*ERROR*/");
                 self.pclose();
             }
+            ast::TyKind::Dummy => {
+                self.popen();
+                self.word("/*DUMMY*/");
+                self.pclose();
+            }
             ast::TyKind::ImplicitSelf => {
                 self.word("Self");
             }