Conflict while backporting issue-less PRs

[ezio-melotti]

I was trying to backport python/cpython#32342 with cherry_picker, and:

• For 3.9/3.10 it added a message about the backport to the original PR, but complained in the checks that the issue number wasn't valid, so I had to remove it from the title
  • [3.10] Update Sphinx bpo role to use redirect URI. cpython#91890
  • [3.9] Update Sphinx bpo role to use redirect URI. cpython#91891
• For 3.7/3.8 it didn't add a message to the original PR, but also didn't complain even with the PR number in the title
  • [3.8] Update Sphinx bpo role to use redirect URI. cpython#91892
  • [3.7] Update Sphinx bpo role to use redirect URI. cpython#91893

All backport PRs had the skip issue (and skip news) labels. I also noticed that the original PR didn't have the needs backport to 3.7/3.8 labels, and after adding them and editing the title to retrigger the check, it added the message and failed the check.

I would expect it to:

• not fail the check if the PR has a skip issue label
• add a message to the original PR even if the needs backport to * label is missing

[DanielNoord]

The first issue is a duplicate of #468 for which I have a fix in #487.

Should probably refocus this issue on the second issue about not posting a message on the original issue for some python versions.

[DanielNoord]

Second issue could be closed by #489.