Automatically mark trunk passing if full test does

[jglick]

An enhancement to #2034: if something like #2066 passes, you ought to be able to trigger a release without redundantly running tests again on trunk. Perhaps Jenkinsfile on master, when run manually (#1993), could first check if the full-tests branch has passing checks, and if so, and it was really solely an empty commit relative to the commit under test (head of main), immediately succeed.