[CI] De-flake tune_scalability_network_overhead [smoketest] (#31580)

**tl;dr**: Timeout is too short. This PR increases the timeout.

`tune_scalability_network_overhead [smoketest]` failed twice recently.

In each case, the test "was successful", But CI failed

Signed-off-by: Balaji Veeramani <balaji@anyscale.com>

release/release_tests.yaml

@@ -1631,7 +1631,7 @@
       cluster_compute: tpl_20x2.yaml
 
     run:
-      timeout: 400
+      timeout: 500
       prepare_timeout: 600
       wait_for_nodes:
         num_nodes: 20