…tation (apache#7464)

The documentation for the `none_failed` trigger rule
(https://airflow.apache.org/docs/stable/concepts.html#trigger-rules)
describes its behavior as "all parents have not failed (`failed` or
`upstream_failed`) i.e. all parents have succeeded or been skipped."
With that definition in mind, there is no reason that the check for
`none_failed` should ever have to check for skipped upstream tasks or
set the current task to `skipped`. The current behavior causes the rule
to skip if all upstream tasks have skipped, which is more than a little
confusing. This fixes the behavior to be consistent with the documentation.

Co-authored-by: root <[email protected]>