Fix AttributeError in lunar_lander.py

[DrRyanHuang]

Description

fix AttributeError of lunar_lander.py

when I run python gymnasium/envs/box2d/lunar_lander.py, it raise,

AttributeError: 'NoneType' object has no attribute 'id'

self.spec is None, so it has no attribute 'id'.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[pseudo-rnd-thoughts]

Could you modify it to replace LunarLander() within the __main__ part to gym.make("LunarLander-v2")

[pseudo-rnd-thoughts]

Thanks for the PR