Always call pdb hook even if tty locking fails

tractor/_debug.py

@@ -471,11 +471,15 @@ async def _breakpoint(
         # we have to figure out how to avoid having the service nursery
         # cancel on this task start? I *think* this works below?
         # actor._service_n.cancel_scope.shield = shield
+        try:
             with trio.CancelScope(shield=True):
                 await actor._service_n.start(
                     wait_for_parent_stdin_hijack,
                     actor.uid,
                 )
+        except RuntimeError:
+            child_release_hook()
+            raise
 
     elif is_root_process():