[k8s] Fix AssertionError in show-gpus when all GPUs were allocated (#… #19037

Job	Run time
python-test (3.8, tests/unit_tests)	3m 25s
python-test (3.8, tests/test_api.py)	37s
python-test (3.8, tests/test_cli.py)	1m 1s
python-test (3.8, tests/test_config.py)	36s
python-test (3.8, tests/test_global_user_state.py)	24s
python-test (3.8, tests/test_jobs.py)	36s
python-test (3.8, tests/test_list_accelerators.py)	46s
python-test (3.8, tests/test_optimizer_dryruns.py)	1m 43s
python-test (3.8, tests/test_optimizer_random_dag.py)	50s
python-test (3.8, tests/test_storage.py)	25s
python-test (3.8, tests/test_wheels.py)	32s
python-test (3.8, tests/test_jobs_and_serve.py)	25s
python-test (3.8, tests/test_yaml_parser.py)	23s
	11m 43s

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