PEP 787: Postpone to Python 3.15

[nhumrich]

Change python version to target 3.15 instead of 3.14

• 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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[hugovk]

Thanks, good luck getting the smaller feature request in for 3.14 🤞