correct the relation in the docstring

src/interface_slurmctld.py

@@ -72,7 +72,7 @@ def is_joined(self) -> bool:
         return True if self.framework.model.relations.get(self._relation_name) else False
 
     def _on_relation_changed(self, event: RelationChangedEvent) -> None:
-        """Get the munge key and slurm_conf from slurmctld on relation joined."""
+        """Get the munge key and slurm_conf from slurmctld on relation changed."""
         if app := event.app:
             if event_app_data := event.relation.data.get(app):