`jsonargparse==4.42.0` causing `test_config_help` failure

[bhimrazy]

jsonargparse==4.42.0 is causing test_config_help failure while it passes untill 4.41.0

(litgpt) ⚡ fix/tests_config_hub ~/litgpt uv pip install jsonargparse==4.41.0
(litgpt) ⚡ fix/tests_config_hub ~/litgpt pytest tests/test_config_hub.py::test_config_help                  
============================================ test session starts =============================================
platform linux -- Python 3.12.11, pytest-8.4.2, pluggy-1.6.0
benchmark: 5.1.0 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
rootdir: /teamspace/studios/this_studio/litgpt
configfile: pyproject.toml
plugins: benchmark-5.1.0, anyio-4.11.0, timeout-2.4.0, rerunfailures-16.1, dependency-0.6.0
collected 46 items                                                                                           

tests/test_config_hub.py ..............................................                                [100%]

======================================= 46 passed, 6 warnings in 9.67s =======================================

(litgpt) ⚡ fix/tests_config_hub ~/litgpt uv pip install jsonargparse==4.42.0
(litgpt) ⚡ fix/tests_config_hub ~/litgpt pytest tests/test_config_hub.py::test_config_help    
.....
error: Parser key "model_config":
  Does not validate against any of the Union subtypes
  Subtypes: [<class 'NoneType'>, <class 'litgpt.config.Config'>]
  Errors:
    - Expected a <class 'NoneType'>
    - Problem with given class_path 'litgpt.Config':
        __args__
  Given value type: <class 'dict'>
  Given value: {'name': 'stories15M', 'hf_config': {}, 'scale_embeddings': False, 'block_size': 256, 'padded_vocab_size': 32000, 'n_layer': 6, 'n_head': 6, 'n_query_groups': 6, 'n_embd': 288, 'head_size': 48, 'rotary_percentage': 1.0, 'parallel_residual': False, 'bias': False, 'norm_class_name': 'RMSNorm', 'mlp_class_name': 'LLaMAMLP', 'intermediate_size': 768}
========================================== short test summary info ===========================================
FAILED tests/test_config_hub.py::test_config_help[litgpt/pretrain.py-pretrain/tinystories.yaml] - SystemExit: 2
FAILED tests/test_config_hub.py::test_config_help[litgpt/pretrain.py-https://raw.githubusercontent.com/Lightning-AI/litgpt/main/config_hub/pretrain/tinystorie