plugin XEP-0376: Fix type hint for node which is optional in subscriptions.

libervia/backend/plugins/plugin_xep_0376.py

@@ -142,7 +142,7 @@ class XEP_0376:
         self,
         client: SatXMPPEntity,
         service: Optional[jid.JID],
-        node: str,
+        node: str|None,
     ) -> Tuple[bool, Optional[List[Dict[str, Any]]]]:
         if not await self.host.has_feature(client, NS_PAM):
             return True, None