Fixing bad suggestion for `_` in `const` type when a function #81885Closes#81885
```
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> $DIR/typeck_type_placeholder_item_help.rs:13:22
|
LL | const TEST4: fn() -> _ = 42;
| ^
| |
| not allowed in type signatures
| help: use type parameters instead: `T`
```
Do not show the suggestion `help: use type parameters instead: T` when `fn`
a6809d00ae