Only set shield flag when trio nursery mode is used

tractor/_discovery.py

@@ -114,15 +114,9 @@ def get_peer_by_name(
     '''
     actor: Actor = current_actor()
     to_scan: dict[tuple, list[Channel]] = actor._peers.copy()
-
-    # TODO: is this ever needed? creates a duplicate channel on actor._peers
-    # when multiple find_actor calls are made to same actor from a single ctx
-    # which causes actor exit to hang waiting forever on
-    # `actor._no_more_peers.wait()` in `_runtime.async_main`
-
-    # pchan: Channel|None = actor._parent_chan
-    # if pchan and pchan.uid not in to_scan:
-    #     to_scan[pchan.uid].append(pchan)
+    pchan: Channel|None = actor._parent_chan
+    if pchan:
+        to_scan[pchan.uid].append(pchan)
 
     for aid, chans in to_scan.items():
         _, peer_name = aid