PYTHON_FOR_REGEN does not allow 3.14 or 3.15

[AA-Turner]

Bug report

Bug description:

See previous update in 500b0f4, #104487, etc.

A

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• GH-137618: Require Python 3.10 to Python 3.15 for PYTHON_FOR_REGEN #137619