fix mypy

Author: maxi297

airbyte_cdk/sources/declarative/retrievers/file_uploader.py

@@ -24,7 +24,7 @@ def __init__(
     def upload(self, record: Record) -> None:
         # TODO validate record shape - is the transformation applied at this point?
         mocked_response = SafeResponse()
-        mocked_response.content = json.dumps(record.data)
+        mocked_response.content = json.dumps(record.data).encode()
         download_target = list(self._download_target_extractor.extract_records(mocked_response))[0]
         if not isinstance(download_target, str):
             raise ValueError(