[nightly] Add decision_tree_autoscaling_20_runs to nightly test

Author: fishbone

release/.buildkite/build_pipeline.py

@@ -67,6 +67,7 @@ def __init__(self, name: str, retry: int = 0):
         # as it hits the scalability limit.
         # "non_streaming_shuffle_1tb_5000_partitions",
         "decision_tree_autoscaling",
+        "decision_tree_autoscaling_20_runs",
         "autoscaling_shuffle_1tb_1000_partitions",
         SmokeTest("stress_test_many_tasks"),
         SmokeTest("stress_test_dead_actors"),