fix: use message=None instead of message="" in job_orchestrator

With the `is not None` checks in `AirbyteTracedException.__str__` (PR #927),
`message=""` returns an empty string instead of falling back to the detailed
`internal_message`. Using `None` lets the fallback work correctly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sophiecuiy

airbyte_cdk/sources/declarative/async_job/job_orchestrator.py

@@ -481,7 +481,7 @@ def create_and_get_completed_partitions(self) -> Iterable[AsyncPartition]:
             # We emitted traced message but we didn't break on non_breaking_exception. We still need to raise an exception so that the
             # call of `create_and_get_completed_partitions` knows that there was an issue with some partitions and the sync is incomplete.
             raise AirbyteTracedException(
-                message="",
+                message=None,
                 internal_message="\n".join(
                     [
                         filter_secrets(exception.__repr__())