### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When attempting to list roles where permission boundaries are attached the response cannot be serialized 

`aws --endpoint-url=http://localhost:4566 iam list-roles --region ap-southeast-2`
```
An error occurred (InternalError) when calling the ListRoles operation (reached max retries: 2): exception while calling iam.ListRoles: Invalid type when serializing AttachedPermissionsBoundary: '<Element 'member' at 0xffff8275ef20>' cannot be parsed to structure.
```

### Expected Behavior

Expect that all roles are listed

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

* Create an IAM policy
* Create an IAM role which used the policy as a permission boundary
* Attempt to list all roles with `aws --endpoint-url=http://localhost:4566 iam list-roles --region ap-southeast-2`


### Environment

```markdown
- OS: MacOS
- LocalStack: latest
```


### Anything else?

_No response_
self, context: RequestContext, user_name: userNameType
    ) -> None:
        if user := get_iam_backend(context).users.get(user_name):
            if hasattr(user, "permissions_boundary"):
                delattr(user, "permissions_boundary")
        else:
            raise NoSuchEntityException()
    def create_user(
        self,
        context: RequestContext,
        user_name: userNameType,
        path: pathType = None,
        permissions_boundary: arnType = None,
        tags: tagListType = None,
    ) -> CreateUserResponse:
        response = call_moto(context=context)
        user = get_iam_backend(context).get_user(user_name)
        if permissions_boundary:
            user.permissions_boundary = permissions_boundary
            response["User"]["PermissionsBoundary"] = AttachedPermissionsBoundary(
                PermissionsBoundaryArn=permissions_boundary,
                PermissionsBoundaryType="Policy",
            )
        return response
    def get_user(