`--sort-reexports` does not retain trailing commas in short `__all__` exports

Hello everyone,

I noticed the --sort-reexports option in the 9.0.0b1 release and wanted to try it out (I hadn't noticed it before).

It works brilliantly, especially in the 9.0.0b1 pre-release, but I noticed that it does not retain trailing commas of an __all__ declaration, even with --profile black. I'm not sure if this is desired behaviour, especially when the __all__ length is too short to trigger black's chopping-down of the entries, but I wanted to at the very least highlight that this happens.

It's not a major problem, but it does clash a bit with the "one-per-line" style of __all__ declaration.

Reproduction:

my_package/__init__.py

from .first import FirstClass
from .second import SecondClass

- __all__ = (
-     "FirstClass",
-     "SecondClass",
- )
+ __all__ = ("FirstClass", "SecondClass")

class FirstClass:
    pass

class SecondClass:
    pass