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.

阅读 pull-request-lifecycle 和 triaging 页面中的“Reviewing”部分，然后检查链接的 CPython pull request 评论中的检查清单。将相关检查清单整合到 pull-request-lifecycle 中，并移除 triaging 中重复的 Reviewing 指导；完成的标准是两个页面不再重复相同的信息。