### 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()}"
        
        assume_role_policy_document = """
        {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Action": "sts:AssumeRole",
              "Principal": "*",
              "Effect": "Allow",
            }
          ]
        }
        """
        with pytest.raises(ClientError) as e:
            aws_client.iam.create_role(
                RoleName=role_name, AssumeRolePolicyDocument=assume_role_policy_document
            )
        snapshot.match("invalid-json", e.value.response)
class TestIAMIntegrations:
    def test_attach_iam_role_to_new_iam_user(self, aws_client):