TST: Skip CI natively, DOC: Update license year

[pllim]

Description

Supposedly, this should Just Work ™️ now...

https://github.blog/changelog/2021-02-08-github-actions-skip-pull-request-and-push-workflows-with-skip-ci/

Direct follow-up of #11168 and #11274 . Also see #11038

Also updated license year, because I needed a second commit to make sure it doesn't skip when second commit doesn't have the directive. Might as well put in a real change, right? Seems to work!

Pros

• Uses built-in functionality, hence reducing our maintenance burden.
• Does not even start any jobs, hence appears to be more eco-friendly (not quantified).

Cons

• There is no way to disable this.
• Skips everything inside .github/workflows, including labeler and triage actions, which is undesirable.
• Might also skip a merge commit in master when PR is merged if the merge commit message collates all PR commit messages into one, and one or more of the PR commits had the trigger in it. See TST: Skip CI natively, DOC: Update license year #11316 (comment)
• Might also skip a cron job run if the last commit in master is a message with the trigger. See TST: Skip CI natively, DOC: Update license year #11316 (comment)

For the first two points in Cons, let's see how actions/runner#976 goes. For the last two points, we might just have to live with it or have a way to scrub out trigger directive from the merge commit message before merge (is that even possible without much pain?).

[pllim]

Oooo... it doesn't even kick off, saving even more CPU cycles!

p.s. Not sure why CircleCI is running but that is out of scope.

[pllim]

Noticed some drawbacks. I will summarize in the original post above.

[saimn]

As you said there is no way to disable this, so I guess we should merge and see how it works for merge commits, cron etc.

[pllim]

Yeah. The way they phrased it though, cron job might be unaffected. We will see about merge in a minute.

Others are complaining too and asking about opting in/out, so we'll see...

[pllim]

Update: Merge commit message only has the PR title, so CI is running. There is still an edge case of what if someone put the directly in PR title but that is so rare (and discouraged) that it isn't really an issue. Seeing this, cron probably will be okay too, since we rarely push directly into master with any skip directive, if at all.