Fix failing test in sentry client unit tests (#280)

Author: NicoHinderling

tests/unit/test_sentry_client_retry.py

@@ -71,6 +71,7 @@ def test_download_artifact_to_file_with_retry_session(self, mock_session_class):
         mock_response = Mock()
         mock_response.status_code = 200
         mock_response.iter_content.return_value = [b"test content"]
+        mock_response.headers = {"Content-Length": "12", "Content-Type": "application/octet-stream"}
         mock_session.get.return_value = mock_response
 
         # Create client with mocked session