### 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 = aws_client.kms.describe_key(KeyId=kms_key["KeyId"])
            assert not key["KeyMetadata"]["Enabled"]
        retry(_is_key_disabled, retries=3, sleep=0.5)
        if is_aws_cloud():
            # time 
            time.sleep(5)
        with pytest.raises(ClientError) as e:
            aws_client.s3.get_(
                Bucket=s3_bucket,
                Key=key_name,
            )
        snapshot.match("get-obj-disabled-key", e.value.response)
        with pytest.raises(ClientError) as e:
            aws_client.s3.put_(
                Bucket=s3_bucket,
                Key="key-is-deactivated",
                Body=data,
                ServerSideEncryption="aws:kms",
                SSEKMSKeyId=kms_key["KeyId"],
            )
        snapshot.match("put-obj-disabled-key", e.value.response)