inplace argument should be optional in ffill() and bfill()

[crusaderky]

mypy 0.961
pandas-stubs 1.4.2.220626

df: pandas.DataFrame
df.ffill()
df.bfill()

output:

error: All overload variants of "ffill" of "DataFrame" require at least one argument  [call-overload]
note: Possible overload variants:
note:     def ffill(self, axis: Optional[Literal['columns', 'index', 0, 1]] = ..., *, inplace: Literal[True], limit: Optional[int] = ..., downcast: Optional[Dict[Any, Any]] = ...) -> None
note:     def ffill(self, axis: Optional[Literal['columns', 'index', 0, 1]] = ..., *, inplace: Literal[False], limit: Optional[int] = ..., downcast: Optional[Dict[Any, Any]] = ...) -> DataFrame
error: All overload variants of "bfill" of "DataFrame" require at least one argument  [call-overload]
note:     def bfill(self, axis: Optional[Literal['columns', 'index', 0, 1]] = ..., *, inplace: Literal[True], limit: Optional[int] = ..., downcast: Optional[Dict[Any, Any]] = ...) -> None
note:     def bfill(self, axis: Optional[Literal['columns', 'index', 0, 1]] = ..., *, inplace: Literal[False], limit: Optional[int] = ..., downcast: Optional[Dict[Any, Any]] = ...) -> DataFrame

From the documentation:

inplace bool, default False

[twoertwein]

I think it might be sufficient to change this line

pandas-stubs/pandas-stubs/core/frame.pyi

Line 1322 in f3e5a49

inplace: Literal[False],

to inplace: Literal[False] = ...,

Feel free to create a PR and add a testcase.