Clean up terminology

[daniel-beck]

The new test unfortunately fails with

java.lang.NullPointerException
	at io.jenkins.plugins.casc.ConfigurationAsCode.lambda$collectProblems$0(ConfigurationAsCode.java:262)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
	at java.base/java.util.HashMap$EntrySpliterator.forEachRemaining(HashMap.java:1764)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497)
	at io.jenkins.plugins.casc.ConfigurationAsCode.collectProblems(ConfigurationAsCode.java:263)
	at io.jenkins.plugins.casc.ConfigurationAsCode.doCheckNewSource(ConfigurationAsCode.java:246)