test(router): ignore deployment-selection logs in the fallback log assertion

simple_shuffle logs the selected deployment at INFO whenever a weight set
applies, so the fallback group's selection line lands between the fallback
notice and the success notice and pushed the notice out of the tail-3 window.
Filter it the same way the neighbouring get_available_deployment noise is
already filtered.

tests/local_testing/test_router_debug_logs.py

@@ -86,6 +86,7 @@ def test_async_fallbacks(caplog):
         if "Task exception was never retrieved" not in log
         and "Task was destroyed but it is pending" not in log
         and "get_available_deployment" not in log
+        and "Selected deployment for model" not in log
         and "in the Langfuse queue" not in log
         and "Unclosed client session" not in log
         and "Unclosed connector" not in log