### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When attempting to sign some document using Localstack KMS inside a lambda container (also running on localstack), the localstack KMS listener returns some unknown error.

The KMS key and lambda containers have been created from the same CDK app deploy, and I can see all the resources in the localstack web console.

The test application I'm using to prove this behaviour is available here:
https://github.com/LukaHedt/localstack_kms_test

Instructions to run are in the main Readme, and the `/localstack/Readme.md` file.

`aws-sdk` returns an unknown error, and the localstack docker logs that I receive are available here:
https://pastebin.com/58Z3fXi3

Have done an amount of testing and can confidently claim the following:
- Have tested on multiple machines with the same outcome
- Doesn’t make a difference if I specify an ARN or a KeyID in the signing request
- Downgrading localstack versions either didn’t make a difference, or I couldn’t actually deploy a localstack container with version 0.12.20 or lower.

### Expected Behavior

KMS Sign should return a signature for the given payload.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

Test application demonstrating the current behaviour is available here:

https://github.com/LukaHedt/localstack_kms_test

Full instructions to run are in the `/localstack/Readme.md` file.


### Environment

```markdown
- OS: MacOS Monteray 12.3
- LocalStack: 0.14.0
```


### Anything else?

_No response_
self, response: dict, operation_model: OperationModel
    ) -> HttpResponse:
        """
        Takes a response dict and serializes it to an actual HttpResponse.
        :param response: to serialize
        :param operation_model: specification of the service & operation containing information about the shape of the
                                service's output / response
        :return: HttpResponse which can be sent to the calling client
        :raises: ResponseSerializerError (either a ProtocolSerializerError or an UnknownSerializerError)
        """
        serialized_response = self._create_default_response(operation_model)
        shape = operation_model.output_shape
        # The shape can also be none (for empty responses), but it still needs to be serialized (to add some metadata)
        shape_members = shape.members if shape is not None else None
        self._serialize_response(
            response, serialized_response, shape, shape_members, operation_model
        )
        serialized_response = self._pional_traits_in_response(
            serialized_response, operation_model
        )
        return serialized_response
    @_handle_exceptions
    def serialize_error_to_response(