[Azure blob] fix `test_private_bucket` for azure blob (#3791) #15504

Job	Run time
python-test (3.8, tests/unit_tests)	6m 26s
python-test (3.8, tests/test_api.py)	3m 57s
python-test (3.8, tests/test_cli.py)	4m 52s
python-test (3.8, tests/test_config.py)	4m 0s
python-test (3.8, tests/test_global_user_state.py)	4m 9s
python-test (3.8, tests/test_jobs.py)	4m 34s
python-test (3.8, tests/test_list_accelerators.py)	4m 10s
python-test (3.8, tests/test_optimizer_dryruns.py)	5m 42s
python-test (3.8, tests/test_optimizer_random_dag.py)	4m 44s
python-test (3.8, tests/test_storage.py)	3m 42s
python-test (3.8, tests/test_wheels.py)	3m 54s
python-test (3.8, tests/test_jobs_and_serve.py)	4m 1s
python-test (3.8, tests/test_yaml_parser.py)	3m 53s
	58m 4s

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