gh-124606: Fix reference leak in error path in datetime_fromisoformat in _datetimemodule.c

[Eclips4]

• Issue: Reference leak in test_datetime #124606

[picnixz]

Thank you for the fix! (though I find the gotos a bit too hard to follow in this specific function). Do you want to run the refleak build bots?

[vstinner]

LGTM.

I confirm that ./python -m test test_datetime -R 3:3 no longer leaks with this change.

For the PR title, you may refer to datetime_fromisoformat() which is more precise ;-)

[vstinner]

Do you want to run the refleak build bots?

It's not needed. I tested manually.