`extend type Foo` where Foo is actually an interface silently fails when it could give a better error
Discord context: https://discord.com/channels/489127045289476126/498852330754801666/1292111166235082803

This is the code I tried to write:

```typescript
// comment on table app.users is $$
//   @interface mode:relational type:kind
//   @type MEMBER references:members
//   @type ADMIN references:admins
// $$;

export const TestPlugin = makeExtendSchemaPlugin(() => {
  return {
    typeDefs: gql`
      extend type User {
        foo1: String
      }

      extend type Member {
        foo2: String
      }

      extend type Admin {
        foo3: String
      }
    `,
    plans: {
      User: {
        // foo1 not in the schema.sql
        foo1() {
          return constant("bar");
        },
      },
      Member: {
        foo2() { // works
          return constant("bar");
        },
      },
      Admin: {
        foo3() { // works
          return constant("bar");
        },
      },
    },
  };
});
```

> That’s coz you’re using extend type which applies to object types; you want extend interface since it’s an interface.
>
> Please file an issue about this; we can be more helpful and throw an error on type mismatch. (Currently the type is never seen so the extension never triggers.)

