chore: fix SyncSourceError test class to implement active_partitions_handler

Signed-off-by: Vaibhav Tiwari <vaibhav.tiwari33@gmail.com>

Author: vaibhavtiwari33

packages/pynumaflow/tests/source/utils.py

@@ -108,7 +108,7 @@ def nack_handler(self, nack_request: NackRequest):
     def pending_handler(self) -> PendingResponse:
         return PendingResponse(count=10)
 
-    def partitions_handler(self) -> PartitionsResponse:
+    def active_partitions_handler(self) -> PartitionsResponse:
         return PartitionsResponse(partitions=mock_partitions())