[python-package] fix mypy errors related to eval result tuples

[jameslamb]

Contributes to #3756.
Contributes to #3867.

Resolves the following errors from mypy:

engine.py:533: error: List comprehension has incompatible type List[Tuple[str, str, floating[Any], bool, floating[Any]]]; expected List[Tuple[str, str, float, bool, float]]  [misc]
engine.py:773: error: Argument "evaluation_result_list" to "CallbackEnv" has incompatible type "List[Tuple[str, str, float, bool, float]]"; expected "Optional[List[Tuple[str, str, float, bool]]]"  [arg-type]

These both came from an incorrect type hint on lightgbm.callback.CallbackEnv.evaluation_result_list, which failed to include the possibility of eval result tuples that included a 5th element for the across-folds standard deviation of metrics, as are calculated in cv().

[jameslamb]

cc @raubitsj @ayulockin I noticed tonight that this issue with the type hints was noticed almost 2 years ago in your development on wandb:

• [WB-7575] Improving wandb_callback for LightGBM (#2945) wandb/wandb#3024
• https://github.com/wandb/wandb/blame/395b0dbebaa90f9e9035d4d9d254000da479f6a8/wandb/integration/lightgbm/__init__.py#L39-L42

First... thanks for your work on that integration, in helping LightGBM's users get the most of their models.

In the future, we'd really appreciate contributions here when you notice issues in LightGBM. Both code contributions and documenting problems at https://github.com/microsoft/LightGBM/issues are very helpful to the project. I'd be happy to help answer any questions you have about contributing, or to hear any critical feedback you have about ways we could improve the contribution process.

[ayulockin]

Thanks for pointing out @jameslamb. It might have slipped out while rapidly developing the integration. Will make sure to open an issue if we spot any.

[github-actions]

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