fix(cdk): change return to break when partition is None to preserve multi-parent behavior

Co-Authored-By: Daryna Ishchenko <darina.ishchenko17@gmail.com>

Author: devin-ai-integration[bot]

airbyte_cdk/sources/declarative/partition_routers/substream_partition_router.py

@@ -208,7 +208,7 @@ def stream_slices(self) -> Iterable[StreamSlice]:
                     parent_stream.generate_partitions()
                 ):
                     if partition is None:
-                        return
+                        break
                     for parent_record, is_last_record_in_slice in iterate_with_last_flag(
                         partition.read()
                     ):