Update "Checklist for Triaging" for GH Issues

[hugovk]

Note: This repo is for the Python devguide. If you are requesting an
enhancementfor the Python language or CPython interpreter,
then the CPython issue tracker is better
suited for this report: https://bugs.python.org

Describe the bug

The "Checklist for Triaging" is outdated as it describes the bpo process.

https://devguide.python.org/triaging/#checklist-for-triaging

Expected behavior

The checklist is updated for GitHub Issues.

Additional context

Most of the fields have been removed and are now replaced with labels or no longer used.

We may need different wording for "classification fields" and "process fields".

Some of the suggestions in the checklist, like editing the title, is not possible for triagers who don't have permission to do so. Although this is still good advice for core devs when triging issues.