Need to keep traceback alive in WITH_EXCEPT_START

[DinoV]

Bug report

Bug description:

Currently in WITH_EXCEPT_START the interpreter loop gets the traceback from the exception object and then immediately decref's it before calling the __exit__ function. But the __exit__ function may not incref the traceback (if it's not an interpretedPython function) and could cause the traceback to be replaced on the exception, leading it holding onto a freed traceback.

CPython versions tested on:

CPython main branch, 3.12

Operating systems tested on:

Linux

Linked PRs

• gh-130595: Keep traceback alive for WITH_EXCEPT_START #130562
• gh-130595: Fix leak in WITH_EXCEPT_START error case #130626

[encukou]

This introduced a refleak, see #130626 for @Fidget-Spinner's fix

[picnixz]

Re-opening as backports were not made.

[picnixz]

Friendly ping @DinoV @Fidget-Spinner Do you want backports for this one?