### 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_
# buck
        bucket_name = f"testuppercase-{short_uid()}"
        s3_create_bucket(Bucket=bucket_name)
        # key 
        _key = "camelCaseKey"
        aws_client.s3.put_(Bucket=bucket_name, Key=_key, Body="something")
        res = aws_client.s3.get_(Bucket=bucket_name, Key=_key)
        snapshot.match("response", res)
        with pytest.raises(ClientError) as e:
            aws_client.s3.get_(Bucket=bucket_name, Key="camelcasekey")
        snapshot.match("wrong-case-key", e.value.response)
    @pytest.mark.skipif(condition=TEST_S3_IMAGE, reason="Lambda not enabled in S3 image")
    @markers.aws.validated
    def test_s3_download__with_lambda(
        self, s3_create_bucket, create_lambda_function, lambda_su_role, aws_client
    ):
        bucket_name = f"bucket-{short_uid()}"
        function_name = f"func-{short_uid()}"
        key = f"key-{short_uid()}"
        s3_create_bucket(Bucket=bucket_name)
        aws_client.s3.put_(Bucket=bucket_name, Key=key, Body="something..")
        create_lambda_function(