### 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_
__init__(self, region_name, account_id, aws_policies=aws_policies)
        self.aws_managed_policies.extend(
            [
                AWSManagedPolicy.from_data(name, self.account_id, d)
                for name, d in ADDITIONAL_MANAGED_POLICIES.items()
            ]
        )
    if "Principal" not in VALID_STATEMENT_ELEMENTS:
        VALID_STATEMENT_ELEMENTS.append("Principal")
    
    @patch(Policy.__init__)
    def policy__init__(
        fn,
        self,
        name,
        account_id,
        default_version_id=None,
        description=None,
        document=None,
        **kwargs,
    ):
        fn(self, name, account_id, default_version_id, description, document, **kwargs)
        self.document = document
    
    @patch(InlinePolicy.unapply_policy)
    def inline_policy_unapply_policy(fn, self, backend):