Dart: sub-packages are not updated

I'm using release-please for dart (I'm using melos https://melos.invertase.dev/)

I have 2 packages (`a`, and `b`). `a` depends on `b`.

Let's say the current versions are:

- `a`: `1.0.0` and depends on `b: ^1.0.0`
- `b`: `1.0.0`

Some `feat` are added to `a` and `b` and the new versions will be
- `a: 1.1.0`
- `b: 1.1.0`

Release-please correctly updates the `pubspec.yaml`s of `a` and `b` to

```diff
+ version: 1.1.0
- version: 1.0.0
```

which is good

But I'd also expect release please to update `a`'s `pubspec.yaml`

```diff
dependencies:
+ b: ^1.1.0
- b: ^1.0.0
```