importlib.resources.abc.Traversable.joinpath is still marked as abstract after implementation

[SamB]

Documentation

importlib.resources.abc.Traversable.joinpath is marked as an abstractmethod, but apparently hasn't been one since:

• gh-97930: Merge with importlib_resources 5.9 #97929

[SamB]

The implications of this in the context of a protocol are too subtle for me to feel up to proposing actual documentation text.

[picnixz]

cc @jaraco