[python-package] [dask] fix mypy errors regarding predict_proba

[IdoKendo]

Contributes to #3867.
Moved from #5672.

mypy currently raises errors regarding predict_proba() method. This PR proposes a fix for it.

Notes for Reviewers

This was tested by running mypy as documented in #3867.

mypy \
    --exclude='python-package/compile/|python-package/build' \
    --ignore-missing-imports \
    python-package/

[jameslamb]

Excellent, thanks!

I can see that mypy finds 84 errors on the latest commit on master (logs link) and 83 here (logs link).

And that this specifically fixed this one:

python-package/lightgbm/dask.py:1258: error: Signature of "predict_proba" incompatible with supertype "LGBMClassifier"  [override]
python-package/lightgbm/dask.py:1258: note:      Superclass:
python-package/lightgbm/dask.py:1258: note:          def predict_proba(self, X: Any, raw_score: bool = ..., start_iteration: int = ..., num_iteration: Optional[int] = ..., pred_leaf: bool = ..., pred_contrib: bool = ..., validate_features: bool = ..., **kwargs: Any) -> Any
python-package/lightgbm/dask.py:1258: note:      Subclass:
python-package/lightgbm/dask.py:1258: note:          def predict_proba(self, X: Union[Any, Any], **kwargs: Any) -> Any

I also see that this signature matches the argument order and default values for LGBMClassifier.

LightGBM/python-package/lightgbm/sklearn.py

Lines 1148 to 1158 in f136de4

	def predict_proba(
	self,
	X,
	raw_score: bool = False,
	start_iteration: int = 0,
	num_iteration: Optional[int] = None,
	pred_leaf: bool = False,
	pred_contrib: bool = False,
	validate_features: bool = False,
	**kwargs: Any
	):

[github-actions]

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