The diagnostic was catching the following case:

```ts
name = signal('Angular');
```

but not the following ones:

```ts
name = signal('Angular').asReadonly();
name = computed(() => 'Angular');
name!: Signal<string>
```

This was not catched in the tests because the type of `Signal` is different than the one actually used in core.
It turns out the real type forces the diagnostic to check both the `symbol.tsType.symbol` and the `symbol.tsType.aliasSymbol`.