nemo_gym 'ActorHandle' object has no attribute 'health_check'

[yuki-97]

Issue
#2741 update Gym but #2759 is still using Gym in old way.

Suggest Fix
Update examples/nemo_gym/run_distillation_nemo_gym.py to mirror the new examples/nemo_gym/run_grpo_nemo_gym.py.

Error Log
https://github.com/NVIDIA-NeMo/RL/actions/runs/27351602878/job/80835736709?pr=2782

2026-06-11T15:31:33.1028798Z Traceback (most recent call last):
2026-06-11T15:31:33.1031109Z   File "/opt/nemo-rl/examples/nemo_gym/run_distillation_nemo_gym.py", line 201, in <module>
2026-06-11T15:31:33.1031629Z     main()
2026-06-11T15:31:33.1031840Z     ~~~~^^
2026-06-11T15:31:33.1032221Z   File "/opt/nemo-rl/examples/nemo_gym/run_distillation_nemo_gym.py", line 175, in main
2026-06-11T15:31:33.1032692Z     ray.get(nemo_gym.health_check.remote())
2026-06-11T15:31:33.1032983Z             ^^^^^^^^^^^^^^^^^^^^^
2026-06-11T15:31:33.1033419Z   File "/opt/nemo_rl_venv/lib/python3.13/site-packages/ray/actor.py", line 2472, in __getattr__
2026-06-11T15:31:33.1033894Z     raise AttributeError(
2026-06-11T15:31:33.1034551Z         f"'{type(self).__name__}' object has " f"no attribute '{item}'"
2026-06-11T15:31:33.1035212Z     )
2026-06-11T15:31:33.1035530Z AttributeError: 'ActorHandle' object has no attribute 'health_check'