fix: use __wrapped__ without self for Celery bind=True tasks in error tests

Celery's __wrapped__ attribute strips the self parameter for bind=True tasks.
Updated error-case tests to call __wrapped__(file_path, ...) instead of
__wrapped__(mock_self, file_path, ...) to avoid 'multiple values' TypeError.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_upload_to_dropbox.py

@@ -199,11 +199,8 @@ class TestUploadToDropbox:
         """Test that missing file raises FileNotFoundError."""
         from app.tasks.upload_to_dropbox import upload_to_dropbox
 
-        mock_self = MagicMock()
-        mock_self.request.id = "test-task"
-
         with pytest.raises(FileNotFoundError):
-            upload_to_dropbox.__wrapped__(mock_self, "/nonexistent/file.pdf", file_id=1)
+            upload_to_dropbox.__wrapped__("/nonexistent/file.pdf", file_id=1)
 
     @patch("app.tasks.upload_to_dropbox.log_task_progress")
     @patch("app.tasks.upload_to_dropbox.settings")