Add note about lack of a guard in missing tag

reporting/src/error/mono.rs

@@ -167,7 +167,8 @@ fn pattern_to_doc_help<'b>(
                         TagName::Global("#Guard".into())
                     );
                     debug_assert!(args.len() == 2);
-                    pattern_to_doc_help(alloc, args[1].clone(), in_type_param)
+                    let tag = pattern_to_doc_help(alloc, args[1].clone(), in_type_param);
+                    tag.append("    (note the lack of a guard)")
                 }
                 RenderAs::Record(field_names) => {
                     let mut arg_docs = Vec::with_capacity(args.len());

reporting/tests/test_reporting.rs

@@ -8486,6 +8486,8 @@ I need all branches in an `if` to have the same type!
             ),
         )
     }
+
+    #[test]
     fn non_exhaustive_with_guard() {
         report_problem_as(
             indoc!(
@@ -8506,7 +8508,7 @@ I need all branches in an `if` to have the same type!
 
                 Other possibilities include:
 
-                    A
+                    A    (note the lack of a guard)
 
                 I would have to crash if I saw one of those! Add branches for them!
                 "#