Fix last_id in fake service when setting dispatches

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/client/dispatch/test/client.py

@@ -53,6 +53,10 @@ def set_dispatches(self, microgrid_id: int, value: list[Dispatch]) -> None:
             value: The list of dispatches to set.
         """
         self._service.dispatches[microgrid_id] = value
+        # Max between last id and the max id in the list
+        self._service._last_id = max(
+            self._service._last_id, max(dispatch.id for dispatch in value)
+        )
 
     @property
     def _service(self) -> FakeService: