### 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_1 = f"role-{short_uid()}"
        role_name_2 = f"role-{short_uid()}"
        assume_role_policy_doc = {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Action": "sts:AssumeRole",
                    "Effect": "Allow",
                    "Principal": {"AWS": ["arn:aws:iam::123412341234:root"]},
                }
            ],
        }
        str_assume_role_policy_doc = json.dumps(assume_role_policy_doc)
        aws_client.iam.create_role(
            Path="/",
            RoleName=role_name_1,
            AssumeRolePolicyDocument=str_assume_role_policy_doc,
        )
        roles = aws_client.iam.list_roles()["Roles"]
        for role in roles:
            if role["RoleName"] == role_name_1:
                assert role["AssumeRolePolicyDocument"] == assume_role_policy_doc
        aws_client.iam.create_role(