Properly clean up timer in stop()

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

Author: Marenz

src/frequenz/dispatch/_bg_service.py

@@ -26,6 +26,7 @@
 from frequenz.client.dispatch.types import DispatchEvent as ApiDispatchEvent
 from frequenz.client.dispatch.types import Event
 from frequenz.sdk.actor import BackgroundService
+from typing_extensions import override
 
 from ._dispatch import Dispatch
 from ._event import Created, Deleted, DispatchEvent, Updated
@@ -225,6 +226,12 @@ async def new_running_state_event_receiver(
 
     # pylint: enable=redefined-builtin
 
+    @override
+    async def stop(self, msg: str | None = None) -> None:
+        """Stop the background service."""
+        self._next_event_timer.stop()
+        await super().stop(msg)
+
     def start(self) -> None:
         """Start the background service."""
         self._tasks.add(asyncio.create_task(self._run()))