Separate PR for root (`.`) package on a mono repos

**Is your feature request related to a problem? Please describe.**

I managed a mono repo that contains root package and sub packages.

```
hello-world.go
modules/
foo/
bar/
```

The `foo` and `bar` packages require the `root` package.

Release please configuraton as follows:

```json
{
"packages": {
".": {
"separate-pull-requests": true,
"exclude-paths": [
"modules"
]
},
"foo": {},
"bar": {},
}
}
```

**Describe the solution you'd like**

I wish release please can open 2 seperated PRs for those releases, but there only one PR, I guess they share and reuse the same branch.

**Describe alternatives you've considered**

**Additional context**