TYP:  ensure_platform_int probably needs a dtype annotation

`ensure_platform_int` is annotated as returning a `np.ndarray` but its output is used in places that require a `Sequence[int]`. I assume this can be fixed by adding a dtype to the `np.ndarray`.

pandas/core/groupby/ops.py:858: error: Argument 1 to "take" of "ExtensionArray" has incompatible type "ndarray[Any, Any]"; expected "Sequence[int]"  [arg-type]