### 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_
# Test 
        # obje
        snapshot.add_transformer(snapshot.transform.key_value("ETag"))
        _key = "sample.bin"
        chunk_size = 1024
        with io.BytesIO() as data:
            data.write(os.urandom(chunk_size * 2))
            data.seek(0)
            aws_client.s3.upload_fileobj(data, s3_bucket, _key)
        range_header = f"bytes=0-{(chunk_size - 1)}"
        resp = aws_client.s3.get_(Bucket=s3_bucket, Key=_key, Range=range_header)
        content = resp["Body"].read()
        assert chunk_size == len(content)
        snapshot.match("get-", resp)
        range_header = f"bytes={chunk_size}-2048"
        resp = aws_client.s3.get_(Bucket=s3_bucket, Key=_key, Range=range_header)
        content = resp["Body"].read()
        assert chunk_size == len(content)
        snapshot.match("get--2", resp)
    @markers.aws.validated
    def test_download_fileobj_multiple_range_(self, s3_bucket, aws_client):