### 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_
# forw
        # (dat
        key = "test-double-headers"
        aws_client.s3.put_(Bucket=s3_bucket, Key=key, Body="test-headers", ACL="public-read")
        key_url = f"{_bucket_url(bucket_name=s3_bucket)}/{key}"
        response = .get(key_url)
        assert response.headers["server"]
        key_url = f"{_bucket_url_vhost(bucket_name=s3_bucket)}/{key}"
        proxied_response = .get(key_url)
        assert proxied_response.ok
        assert proxied_response.headers["server"] == response.headers["server"]
        assert len(proxied_response.headers["server"].split(",")) == 1
        assert len(proxied_response.headers["date"].split(",")) == 2  # coma 
    @pytest.mark.skipif(condition=TEST_S3_IMAGE, reason="KMS not enabled in S3 image")
    @markers.aws.validated
    def test_s3_sse_validate_kms_key(