fix: Remove unused MagicMock imports to pass ruff linter

- Remove unused MagicMock import from test_dialog_service.py
- Remove unused MagicMock import from test_conversation_service.py
- Remove unused MagicMock import from test_canvas_service.py

Fixes CI linting errors (F401: imported but unused)

test/unit_test/services/test_canvas_service.py

@@ -16,7 +16,7 @@
 
 import pytest
 import json
-from unittest.mock import Mock, patch, MagicMock, AsyncMock
+from unittest.mock import Mock, patch, AsyncMock
 from common.misc_utils import get_uuid
 
 

test/unit_test/services/test_conversation_service.py

@@ -15,7 +15,7 @@
 #
 
 import pytest
-from unittest.mock import Mock, patch, MagicMock
+from unittest.mock import Mock, patch
 from common.misc_utils import get_uuid
 
 

test/unit_test/services/test_dialog_service.py

@@ -15,7 +15,7 @@
 #
 
 import pytest
-from unittest.mock import Mock, patch, MagicMock
+from unittest.mock import Mock, patch
 from common.misc_utils import get_uuid
 from common.constants import StatusEnum