Adhere to PEP 685 when evaluating markers with extras

[hroncok]

PEP: https://peps.python.org/pep-0685/
Original problem: https://discuss.python.org/t/7614

Part of #526

[brettcannon]

LGTM, just want to simplify the code a bit.

[brettcannon]

FYI I have an in-progress PR that also normalizes the value so that the string representation is fully normalized. But I like the solution for this part of it by @hroncok more than mine. 🙂

[hroncok]

There is a fixup commit now. Please squash when (or before) merging or tell me to do it when ready.

[pradyunsg]

Please go ahead and squash.

I learnt this recently: If you make a force-push with a single commit amended, it's possible to see what you've changed in the force-push -- by clicking "force-pushed" text in the event that GitHub adds. This is useful for exactly the situation we have here -- a single commit fixup. :)

[brettcannon]

The change LGTM, so like Pradyun said, please go ahead and squash. 🙂

[hroncok]

Done.