Fix test for future versions of jenkins - PCT failures

[res0nance]

Due to jenkinsci/jenkins#5275 a test breaks PCT and is blocking jenkinsci/bom#511.

Adapt the test to work for the plugin's version of jenkins and for the later releases of jenkins

Tested manually with mvn clean install -Djenkins.version=2.289

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[timja]

@dwnusbaum @car-roll @bitwiseman @jglick

[jglick]

Remember that for #92 to work you need to label PRs like this.