### 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, params: dict, shape: Shape, operation_model: OperationModel
    ) -> ETree.Element:
        # The Query protocol responses have a root element which is not contained in the specification file.
        # Therefore we first call the super function to perform the normal XML serialization, and afterwards wrap the
        # result in a root element based on the operation name.
        node = super()._serialize_body_params_to_xml(params, shape, operation_model)
        # Check if we need to add a namespace
        attr = (
            {"xmlns": operation_model.metadata.get("xmlNamespace")}
            if "xmlNamespace" in operation_model.metadata
            else None
        )
        # Create the root element and add the result of the XML serializer as a child node
        root = ETree.Element(f"{operation_model.name}Response", attr)
        if node is not None:
            root.append(node)
        return root
    def _pional_traelf, rootree.Element]):
        # Add the response metadata here (it's not defined in the specs)
        # For the ec2 and the query protocol, the root cannot be None at this time.
        response_metadata = ETree.SubElement(root, "ResponseMetadata")
        request_id = ETree.SubElement(response_metadata, "RequestId")
        request_id.text = gen_amzn_requestid_long()
class EC2ResponseSerializer(QueryResponseSerializer):
    """