Fix Compressed tensors to_dict_diff

[MekkCyber]

What does this PR do?

When creating the dict config, checks if the key exists in the defaut config before trying to access its value.
It was causing the error :

File "./transformers/src/transformers/utils/quantization_config.py", line 1364, in to_diff_dict
    if value != default_config_dict[key]:
                ~~~~~~~~~~~~~~~~~~~^^^^^
KeyError: 'config_groups'

[github-actions]

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[SunMarc]

Thx !

[HuggingFaceDocBuilderDev]

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