### 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,
        error: ServiceException,
        code: str,
        sender_fault: bool,
        response: HttpResponse,
        shape: Shape,
        operation_model: OperationModel,
    ) -> None:
        # TODO handle error shapes with members
        # Check if we need to add a namespace
        attr = (
            {"xmlns": operation_model.metadata.get("xmlNamespace")}
            if "xmlNamespace" in operation_model.metadata
            else {}
        )
        root = ETree.Element("ErrorResponse", attr)
        error_tag = ETree.SubElement(root, "Error")
        self._add_error_tags(code, error, error_tag, sender_fault)
        request_id = ETree.SubElement(root, "RequestId")
        request_id.text = gen_amzn_requestid_long()
        response.data = self._encode_payload(self._
    def _add_error_tags(
        self, code: str, error: ServiceException, error_tag: ETree.Element, sender_fault: bool
    ) -> None:
        code_tag = ETree.SubElement(error_tag, "Code")
        code_tag.text = code
        message = self._get_error_message(error)
        if message:
            self._default_serialize(error_tag, message, None, "Message")
        if sender_fault: