### 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_
role_name = f"role-{short_uid()}"
        policy_name = f"policy={short_uid()}"
        session_name = f"session-{short_uid()}"
        account_arn = aws_client.sts.get_caller_identity()["Arn"]
        assume_policy_doc = {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Action": "sts:AssumeRole",
                    "Principal": {"AWS": account_arn},
                    "Effect": "Allow",
                }
            ],
        }
        created_role_arn = create_role(
            RoleName=role_name, AssumeRolePolicyDocument=json.dumps(assume_policy_doc)
        )["Role"]["Arn"]
        aws_client.iam.put_role_policy(
            RoleName=role_name, PolicyName=policy_name, PolicyDocument=GET_USER_POLICY_DOC
        )
        keys = wait_and_assume_role(role_arn=created_role_arn, session_name=session_name)
        iam_client_as_role = create_client_with_keys("iam", keys=keys)
        with pytest.raises(ClientError) as e:
            iam_client_as_role.get_user()
        e.match("Must specify userName when calling with non-User credentials")
    def test_create_user_with_permission_boundary(self, create_user, create_policy, aws_client):