### 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_
hash_sha1,
    hash_sha256,
    long_uid,
    short_uid,
    to_bytes,
    to_str,
)
from localstack.utils.sync import retry
from localstack.utils.testutil import check_expected_lambda_log_events_length
from localstack.utils.urls import localstack_host as get_localstack_host
from tests.aws.services.s3.conftest import TEST_S3_IMAGE
if TYPE_CHECKING:
    from mypy_boto3_s3 import S3Client
LOG = logging.getLogger(__name__)
HEADER_TRANSFORMER = [
    TransformerUtility.jsonpath("$..HTTPHeaders.date", "date", reference_replacement=False),
    TransformerUtility.jsonpath(
        "$..HTTPHeaders.last-modified", "last-modified", reference_replacement=False
    ),
    TransformerUtility.jsonpath("$..HTTPHeaders.server", "server", reference_replacement=False),
    TransformerUtility.jsonpath("$..HTTPHeaders.x-amz-id-2", "id-2", reference_replacement=False),
    TransformerUtility.jsonpath(
        "$..HTTPHeaders.x-amz-request-id", "request-id", reference_replacement=False
    ),
    TransformerUtility.key_value("HostId", reference_replacement=False),
    TransformerUtility.key_value("RequestId", reference_replacement=False),
]
S3_ASSUME_ROLE_POLICY = {
    "Version": "2012-10-17",
    "Statement": [