### 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_
snapshot.add_transformer(snapshot.transform.iam_api())
        snapshot.add_transformer(snapshot.transform.resource_name("role_name"))
        snapshot.add_transformer(snapshot.transform.key_value("RoleId", "role_id"))
        policy = {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Principal": {"Service": ["ec2.amazonaws.com"]},
                    "Action": ["sts:AssumeRole"],
                }
            ],
        }
        role_name = f"role-{short_uid()}"
        result = aws_client.iam.create_role(
            RoleName=role_name,
            AssumeRolePolicyDocument=json.dumps(policy),
        )
        snapshot.match("created_role", result)
        try:
            result = aws_client.iam.update_assume_role_policy(
                RoleName=role_name,
                PolicyDocument=json.dumps(policy),
            )
            snapshot.match("updated_policy", result)
        finally:
            aws_client.iam.delete_role(RoleName=role_name)