updated return object type

lib/charms/grafana_k8s/v0/grafana_source.py

@@ -429,13 +429,15 @@ def update_source(self, source_url: Optional[str] = ""):
                 continue
             self._set_sources(rel)
 
-    def get_source_uids(self) -> Dict[Relation, Dict[str, str]]:
-        """Get the datasource UID(s) assigned by the remote end(s) to this datasource."""
+    def get_source_uids(self) -> Dict[str, Dict[str, str]]:
+        """Get the datasource UID(s) assigned by the remote end(s) to this datasource.
+
+        Returns a mapping from remote application names to unit names to datasource uids."""
         uids = {}
         for rel in self._charm.model.relations.get(self._relation_name, []):
             if not rel:
                 continue
-            uids[rel] = json.loads(rel.data[rel.app]["datasource_uids"])
+            uids[rel.app.name] = json.loads(rel.data[rel.app]["datasource_uids"])
         return uids
 
     def _set_sources_from_event(self, event: RelationJoinedEvent) -> None: