Add Throttle Concurrent Builds to the managed set

[basil]

Although this plugin is not used as a dependency very often, I think it would be desirable to have it included in the BOM inasmuch as this results in increased compatibility testing.

[timja]

hmm, this failed on master https://github.com/jenkinsci/bom/runs/2813164559

[basil]

That test passes locally with PLUGINS=throttle-concurrents TEST=hudson.plugins.throttleconcurrents.ThrottleJobPropertyFreestyleTest bash local-test.sh. I think it's just flaky. Let me see if I can debug it.

[basil]

That test passes locally with PLUGINS=throttle-concurrents TEST=hudson.plugins.throttleconcurrents.ThrottleJobPropertyFreestyleTest bash local-test.sh. I think it's just flaky. Let me see if I can debug it.

=> jenkinsci/throttle-concurrent-builds-plugin#130

I'll release that and then open a PR to update Throttle Concurrent Builds in the BOM to the new version where the flaky test is fixed.

[basil]

I'll release that and then open a PR to update Throttle Concurrent Builds in the BOM to the new version where the flaky test is fixed.

=> #555