https://github.com/localstack/localstack/blob/e7efc768a20e75feafe3702a5a6e477a233feff2/localstack/utils/aws/aws_stack.py#L904

```
File "/usr/local/lib/python3.8/site-packages/localstack/services/generic_proxy.py", line 50, in <module>
from localstack.utils.aws import aws_stack
File "/usr/local/lib/python3.8/site-packages/localstack/utils/aws/aws_stack.py", line 904, in <module>
) -> dict[str, str]:
TypeError: 'type' object is not subscriptable
```

Please fix to `Dict[str, str]`
request.headers.add_header(HEADER_LOCALSTACK_ACCOUNT_ID, get_aws_account_id())
            event_system = new_client.meta.events
            event_system.register_first("before-sign.*.*", _add_internal_header)
        if cache:
            BOTO_CLIENTS_CACHE[cache_key] = new_client
        return new_client
def create_external_boto_client(