Fix `nest_from_op()` call sigs, already changed upstream

In `._runtime/_root` and since the latest fn-signature changes were
already landed onto main branch via the 65b7956: #384-patch.

tractor/_root.py

@@ -521,7 +521,7 @@ async def open_root_actor(
 
                     op_nested_actor_repr: str = _pformat.nest_from_op(
                         input_op='>) ',
-                        tree_str=actor.pformat(),
+                        text=actor.pformat(),
                         nest_prefix='|_',
                     )
                     logger.info(

tractor/_runtime.py

@@ -1690,9 +1690,9 @@ async def async_main(
 
     op_nested_actor_repr: str = _pformat.nest_from_op(
         input_op=')> ',
-        tree_str=actor.pformat(),
+        text=actor.pformat(),
         nest_prefix='|_',
-        back_from_op=2,
+        nest_indent=2,
     )
     teardown_report += (
         'Actor runtime exited\n'