DiffEntry has no sha when permission changes

[jayjoshi64]

Reproduce steps:

1. Create a commit which has permission changed. No changes in the file content.
2. Try to get the commit using compare_commits

github.rest.repos.compare_commits(
    owner="test",
    repo=""test,
    basehead="abcabcabcabc~1...abcabcabcabc"
).parsed_data

Fails with

--->  ).parsed_data
File [/usr/local/lib/python3.10/site-packages/githubkit/response.py:94](githubkit/response.py:94), in Response.parsed_data(self)
     [92](githubkit/response.py:92) @property
     [93](githubkit/response.py:93) def parsed_data(self) -> MT:
---> [94](githubkit/response.py:94)     return type_validate_json(self._data_model, self.content)

File [/usr/local/lib/python3.10/site-packages/githubkit/compat.py:43](githubkit/compat.py:43), in type_validate_json(type_, data)
     [42](githubkit/compat.py:42) def type_validate_json(type_: type[T], data: Any) -> T:
---> [43](githubkit/compat.py:43)     return TypeAdapter(type_).validate_json(data)

File [/usr/local/lib/python3.10/site-packages/pydantic/type_adapter.py:135](pydantic/type_adapter.py:135), in _frame_depth.<locals>.wrapper.<locals>.wrapped(self, *args, **kwargs)
    [132](pydantic/type_adapter.py:132) @wraps(func)
    [133](pydantic/type_adapter.py:133) def wrapped(self: TypeAdapterT, *args: P.args, **kwargs: P.kwargs) -> R:
    [134](pydantic/type_adapter.py:134)     with self._with_frame_depth(depth + 1):  # depth + 1 for the wrapper function
--> [135](pydantic/type_adapter.py:135)         return func(self, *args, **kwargs)

File [/usr/local/lib/python3.10/site-packages/pydantic/type_adapter.py:384](pydantic/type_adapter.py:384), in TypeAdapter.validate_json(self, data, strict, context)
    [368](pydantic/type_adapter.py:368) @_frame_depth(1)
    [369](pydantic/type_adapter.py:369) def validate_json(
    [370](pydantic/type_adapter.py:370)     self, data: str | bytes, [/](None = None, context: dict[str, Any] | None = None
    [371](pydantic/type_adapter.py:371) ) -> T:
    [372](pydantic/type_adapter.py:372)     """Usage docs: https://docs.pydantic.dev/2.9/concepts/json/#json-parsing
    [373](pydantic/type_adapter.py:373) 
    [374](pydantic/type_adapter.py:374)     Validate a JSON string or bytes against the model.
   (...)
    [382](pydantic/type_adapter.py:382)         The validated object.
    [383](pydantic/type_adapter.py:383)     """
--> [384](pydantic/type_adapter.py:384)     return self.validator.validate_json(data, strict=strict, context=context)

ValidationError: 2 validation errors for CommitComparison
files.literal[<UNSET>]
  Input should be <UNSET> [type=literal_error, input_value=[{'sha': 'abcabcabc...'}], input_type=list]
    For further information visit https://errors.pydantic.dev/2.9/v/literal_error
files.list[DiffEntry].2.sha
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]
    For further information visit https://errors.pydantic.dev/2.9/v/string_type

Tha main changes in the endpoint is that there's no SHA for the file change:

{'sha': None,     <--- This is the issue
   'filename': 'test.py',
   'status': 'modified',
   'additions': 0,
   'deletions': 0,
   'changes': 0,
   'blob_url': '. . .',
   'raw_url': '. . .',
   'contents_url': '. . .'
}

[yanyongyu]

The diff-entry object's sha field can be None. Could you please also report this to https://github.com/github/rest-api-description/? I will make a schema patch to fix this in githubkit.

[jayjoshi64]

created: github/rest-api-description#4652

@yanyongyu , I am new to rest-api-description. Feel free to add any details that I missed, thanks.