Make argument which we do not use optional

Author: avandras

patroni/multisite.py

@@ -63,7 +63,7 @@ def status(self) -> Dict[str, Any]:
     def should_failover(self) -> bool:
         return False
 
-    def on_shutdown(self, checkpoint_location: int):
+    def on_shutdown(self, checkpoint_location: Optional[int]):
         pass
 
 
@@ -172,7 +172,7 @@ def release(self):
     def should_failover(self):
         return self._failover_target is not None and self._failover_target != self.name
 
-    def on_shutdown(self, checkpoint_location: int):
+    def on_shutdown(self, checkpoint_location: Optional[int]):
         """ Called when shutdown for multisite failover has completed.
         """
         # TODO: check if we replicated everything to standby site