Improve expectation for platform requires mismatch

```
── TYPE MISMATCH ───── examples/hello-world/rust-platform/./Package-Config.roc ─

Something is off with the type annotation of the main required symbol:

2│      requires {} { main : a -> a }
                             ^^^^^^

This #UserApp.main value is a:

    Str

But the type annotation on main says it should be:

    a -> a

────────────────────────────────────────────────────────────────────────────────
```

compiler/constrain/src/module.rs

@@ -155,7 +155,7 @@ fn constrain_symbols_from_requires(
                     Expected::FromAnnotation(
                         loc_symbol.map(|&s| Pattern::Identifier(s)),
                         arity,
-                        AnnotationSource::TypedBody {
+                        AnnotationSource::RequiredSymbol {
                             region: loc_type.region,
                         },
                         loc_type.value,