### 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_
matching_item = comparison_set.find_item(item)
        if matching_item == item:
            return
        
        if comparison_set == after:
            if matching_item:
                return
            event_name = "REMOVE"
        else:
            event_name = "INSERT" if not matching_item else "MODIFY"
        old_image = item if event_name == "REMOVE" else matching_item
        new_image = matching_item if event_name == "REMOVE" else item
        
        keys = SchemaExtractor.extract_keys_for_schema(item=item, key_schema=key_schema)
        record = {
            "eventName": event_name,
            "dynamodb": {
                "Keys": keys,
                "NewImage": new_image,
                "SizeBytes": len(json.dumps(item)),
                "eventID": short_uid(),
            },
        }
        if stream_spec:
            record["dynamodb"]["StreamViewType"] = stream_spec["StreamViewType"]
        if old_image:
            record["dynamodb"]["OldImage"] = old_image
        result.append(record)
    
    for item in after.items_list: