plugin XEP-0084: Fix entity updated:

`on_metadata_update` was wrongly using our own JID instead of the PEP sender's one.

libervia/backend/plugins/plugin_xep_0084.py

@@ -82,7 +82,7 @@ class XEP_0084:
     async def on_metadata_update(
         self, client: SatXMPPEntity, itemsEvent: pubsub.ItemsEvent
     ) -> None:
-        entity = client.jid.userhostJID()
+        entity = itemsEvent.sender
         avatar_metadata = await self.get_avatar(client, entity)
         await self._i.update(client, IMPORT_NAME, "avatar", avatar_metadata, entity)