[JENKINS-61290] hard to see why a branch was not inspected - log them

[jimklimov]

Your checklist for this pull request

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side) and not your master branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or in Jenkins JIRA
• Link to relevant pull requests, esp. upstream and downstream changes
• Did you provide a test-case? That demonstrates feature works or fixes the issue.

• JENKINS issue(s):
  • https://issues.jenkins-ci.org/browse/JENKINS-61290
• Description:
  • When branch is not indexed/scanned because of policy setting, it is not easy to see why it was skipped. This PR adds logging of isExcluded() hits into global jenkins log. Alas, I did not find a way to log it into the indexing run's log itself where it would be more appropriate.
• Documentation changes:
  • No doc change proposed at this time, as this is a small change for trace-logging and no new/changed feature.
• Users/aliases to notify:
  • markewaite

Solution:

• BranchDiscoveryTrait.java : report into scan log if a branch is ignored (because it is or is-not a source of PR, based on user choice of settings) similarly as proposed and refined for github-branch-source-plugin in [JENKINS-61290] hard to see why a branch was not inspected - log them github-branch-source-plugin#284

Currently there is no test-case proposed for this change, as this is a small change for trace-logging and no new/changed feature. (And trying to make a test case in the github version of the plugin stalled the PR so I'm a bit fearful of this)

[jimklimov]

Trying to trigger the rebuild, hoping jenkins-infra is fixed now.

[lifeofguenter]

lgtm!