Pipeline-utility-steps tests fails when upgrading workflow-api from 2.30 to 2.31

I was trying to run this plugin on PCT on Java 11, but realized this would fail also on Java 8. Demonstrated in https://github.com/jenkinsci/pipeline-utility-steps-plugin/pull/60

This would be good to fix this plugin so it runs correctly on Java 8, and then we can test its behaviour on Java 11.

Acceptance criteria

PCT run should be successful. Command:

docker run --rm -v maven-repo:/root/.m2 -v $PWD/out:/pct/out -e ARTIFACT_ID=pipeline-utility-steps -e VERSION=pipeline-utility-steps-2.2.0