chore: update GHA guide

[henryiii]

This updates the GHA guide a bit with non-controversial changes (hopefully). I think using pipx instead of the current setup would be simpler and is better practice, I might do that in a followup.

Changes:

• Point out this works only for pure Python, link to cibuildwheel for binary packages
• Use Python 3.x
• Drop mention about needed pyproject.toml to use build and links to PEPs (it is backward compatible if it's missing)
• Use more recent versions of actions and the tagged versions of all actions

[webknjaz]

I've put some suggestions below plus a portion of these changes has been merged via another recent PR making conflicts resolution necessary too.

[hugovk]

See #1221 to fix the linkcheck.

[webknjaz]

Thanks for all the effort you've put into this!