PEP 803: Position abi3t as a new variant; use Py_GIL_DISABLED to select it

[encukou]

• Change is either:
  • To a Draft PEP
  • To an Accepted or Final PEP, with Steering Council approval
  • To fix an editorial issue (markup, typo, link, header, etc)
• PR title prefixed with PEP number (e.g. PEP 123: Summary of changes)

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📚 Documentation preview 📚: https://pep-previews--4747.org.readthedocs.build/

[rgommers]

Thanks for this update @encukou. I will comment on DPO with a few thoughts, but while reading thought it'd be useful to notice the textual little things that could be improved - hence this review.

[encukou]

Thank you!