Assertion bug: 'a is! Set && b is! Set': iterableEquals doesn't support Sets

I have a nested object that, when compared, calls `objectsEquals` internally and in turn `iterableEquals`.

In my case, `a` is `Iterable` and `b` is `Set`, so the following code calls `iterableEquals`:

```dart
} else if (a is Set && b is Set) {
return setEquals(a, b);
} else if (a is Iterable && b is Iterable) {
return iterableEquals(a, b);
}
```

However, inside `iterableEquals` I get the assertion error because `'a is! Set && b is! Set'` is `true`.