### 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_
data="test_data",
            headers={"Content-Type": "text/xml"},
        )
        assert response.status_code == 403
        exception = xmltodict.parse(response.content)
        exception["StatusCode"] = response.status_code
        snapshot.match("content-type-exception", exception)
        if signature_version == "s3":
            # we s
            # (tim
            time.sleep(1.1)
        # rege
        presigned_url = presigned_client.generate_presigned_url(
            "put_",
            Params={
                "Bucket": s3_bucket,
                "Key": _key,
                "ContentEncoding": "identity",
            },
            ExpiresIn=10,
        )
        # send 
        response = .put(
            presigned_url,
            data="test_data",
            headers={"Content-Encoding": "identity"},
        )
        assert not response.content
        assert response.status_code == 200
        # send