### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
Key=key_name,
            Body=data,
            ServerSideEncryption="aws:kms",
            SSEKMSKeyId=kms_key["KeyId"],
        )
        snapshot.match("success-put--sse", put__with_sse)
        get__with_sse = aws_client.s3.get_(
            Bucket=s3_bucket,
            Key=key_name,
        )
        snapshot.match("success-get--sse", get__with_sse)
        # disa
        aws_client.kms.disable_key(KeyId=kms_key["KeyId"])
        # test 
        if not is_aws_cloud():
            get_ = aws_client.s3.get_(Bucket=s3_bucket, Key=key_name)
            assert get_["ResponseMetadata"]["HTTPStatusCode"] == 200
            response = aws_client.s3.put_(
                Bucket=s3_bucket,
                Key="test-sse-kms-disabled-key-no-check",
                Body=data,
                ServerSideEncryption="aws:kms",
                SSEKMSKeyId=kms_key["KeyId"],
            )
            assert response["ResponseMetadata"]["HTTPStatusCode"] == 200
        # acti
        monkeypatch.setattr(config, "S3_SKIP_KMS_KEY_VALIDATION", False)
        # disa
        aws_client.kms.disable_key(KeyId=kms_key["KeyId"])
        def _is_key_disabled():