### 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_
params = {
            "Bucket": bucket,
            "Key": key,
            "Body": data,
            "ChecksumAlgorithm": algorithm,
            f"Checksum{algorithm}": short_uid(),
        }
        with pytest.raises(ClientError) as e:
            aws_client.s3.put_(**params)
        snapshot.match("put-wrong-checksum", e.value.response)
        error = e.value.response["Error"]
        assert error["Code"] == "InvalidRequest"
        checksum_header = f"x-amz-checksum-{algorithm.lower()}"
        assert error["Message"] == f"Value for {checksum_header} header is invalid."
        # Te
        match algorithm:
            case "CRC32":
                checksum = checksum_crc32(data)
            case "CRC32C":
                checksum = checksum_crc32c(data)
            case "SHA1":
                checksum = hash_sha1(data)
            case "SHA256":
                checksum = hash_sha256(data)
            case _:
                checksum = ""
        params.update({f"Checksum{algorithm}": checksum})
        response = aws_client.s3.put_(**params)
        snapshot.match("put--generated", response)
        assert response["ResponseMetadata"]["HTTPStatusCode"] == 200