chore: update PyPI URL for official nightly pyarrow repository

[raulcd]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
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• Appropriate docs were updated (if necessary)

Fixes #2222 🦕

[google-cla]

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[raulcd]

I am a downstream Arrow committer. I think I just signed the CLA, let me know if there's anything else to do.
Thanks!

[Linchin]

Thanks a lot for making the correction.

[chalmerlowe]

LGTM