Improve PR review checklist

In https://github.com/python/cpython/pull/93823#issuecomment-1156152572 @erlend-aasland wrote a checklist about reviewing PRs.

In https://github.com/python/devguide/pull/914#issuecomment-1207257987, I suggested:

SGTM -- that's a nice list. I think it would be easier to add it in a separate PR though.
Reviewing PRs is currently documented in two places:

• https://devguide.python.org/getting-started/pull-request-lifecycle/#reviewing
• https://devguide.python.org/triage/triaging/#reviewing-patches

The former has been likely written from scratch after the HG->Git migration, whereas the latter formerly documented how to review patches attached to a bpo issue and then it has been adapted to GitHub. I think the best approach would be to enhance the pull-request-lifecycle with your list, and remove the duplicated info in triaging.

Leggi le sezioni «Reviewing» delle pagine pull-request-lifecycle e triaging, quindi esamina la checklist nel commento collegato della pull request di CPython. Consolida la checklist pertinente in pull-request-lifecycle e rimuovi le indicazioni duplicate sul Reviewing da triaging; il lavoro è completato quando le due pagine non riportano più le stesse informazioni.