Sync with upcoming typeshed changes making slice hashable

[bersbersbers]

As a heads-up:

pandas-stubs (https://github.com/pandas-dev/pandas-stubs)
+ pandas-stubs/core/frame.pyi:608: error: Overloaded function signatures 2 and 3 overlap with incompatible return types  [overload-overlap]

I guess this is acceptable - pandas-stubs has # type: ignore[overload-overlap] # pyright: ignore[reportOverlappingOverload] in line 606 already, and with this PR, they likely need it in line 608 as well:

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

Lines 605 to 610 in f71224c

	@overload
	def __getitem__(self, key: Scalar | tuple[Hashable, ...]) -> Series: ... # type: ignore[overload-overlap] # pyright: ignore[reportOverlappingOverload]
	@overload
	def __getitem__(self, key: Iterable[Hashable] | slice) -> DataFrame: ...
	@overload
	def __getitem__(self, key: Hashable) -> Series: ...

Originally posted by @bersbersbers in python/typeshed#12832 (comment)