### 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_
key_name = "test-key"
        aws_client.s3.put_(Bucket=s3_bucket, Key=key_name, Tagging="tag1=tag1")
        # GetO
        get__tagging_url = f"{bucket_url}/{key_name}?tagging"
        resp = s3_http_client.get(get__tagging_url, headers=headers)
        resp_dict = xmltodict.parse(resp.content)
        assert resp_dict["Tagging"]["TagSet"] == {"Tag": {"Key": "tag1", "Value": "tag1"}}
        assert resp_dict["Tagging"]["@xmlns"] == "http://s3.amazonaws.com/doc/2006-03-01/"
        # Copy
        get__tagging_url = f"{bucket_url}/{key_name}?tagging"
        resp = s3_http_client.get(get__tagging_url, headers=headers)
        resp_dict = xmltodict.parse(resp.content)
        assert resp_dict["Tagging"]["TagSet"] == {"Tag": {"Key": "tag1", "Value": "tag1"}}
        assert resp_dict["Tagging"]["@xmlns"] == "http://s3.amazonaws.com/doc/2006-03-01/"
        copy__url = f"{bucket_url}/copied-key"
        copy__headers = {**headers, "x-amz-copy-source": f"{bucket_url}/{key_name}"}
        resp = s3_http_client.put(copy__url, headers=copy__headers)
        resp_dict = xmltodict.parse(resp.content)
        assert "CopyResult" in resp_dict
        assert resp_dict["CopyResult"]["@xmlns"] == "http://s3.amazonaws.com/doc/2006-03-01/"
        multipart_key = "multipart-key"
        create_multipart = aws_client.s3.create_multipart_upload(
            Bucket=s3_bucket, Key=multipart_key
        )
        upload_id = create_multipart["UploadId"]
        upload_part_url = f"{bucket_url}/{multipart_key}?UploadId={upload_id}&PartNumber=1"
        resp = s3_http_client.put(upload_part_url, headers=headers)
        assert not resp.content, resp.content
    @markers.aws.validated
    def test_s3_timestamp_precision(self, s3_bucket, aws_client, aws_http_client_factory):