Test: Added test cases for Delete Chat Assistants HTTP API (#6879)

### What problem does this PR solve?

cover [delete chat
assistants](https://ragflow.io/docs/dev/http_api_reference#delete-chat-assistants)
endpoints

### Type of change

- [x] add test cases

sdk/python/test/test_http_api/test_dataset_mangement/test_delete_datasets.py

@@ -13,7 +13,6 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 #
-
 from concurrent.futures import ThreadPoolExecutor
 
 import pytest