Minor: Extend documentation phrasing

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

Author: Marenz

src/frequenz/dispatch/_bg_service.py

@@ -337,7 +337,7 @@ async def _run(self) -> None:
                             pass
 
     async def _execute_scheduled_event(self, dispatch: Dispatch, timer: Timer) -> None:
-        """Execute a scheduled event.
+        """Execute a scheduled event and schedules the next one if any.
 
         Args:
             dispatch: The dispatch to execute.