### 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_
import json
import pytest
from botocore.exceptions import ClientError
from localstack.aws.accounts import get_aws_account_id
from localstack.aws.api.iam import Tag
from localstack.services.iam.provider import ADDITIONAL_MANAGED_POLICIES
from localstack.testing.aws.util import create_client_with_keys, wait_for_user
from localstack.utils.common import short_uid
from localstack.utils.strings import long_uid
GET_USER_POLICY_DOC = """{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "sgetuser",
            "Effect": "Allow",
            "Action": ["iam:GetUser"],
            "Resource": "*"
        }
    ]
}"""
class TestIAMExtensions: