[BUG] ConcurrentModificationException error after scala test suite completes

[andygrove]

Describe the bug
I've noticed this error a few times lately after the Scala test suite completes.

Exception in thread "Thread-7" java.util.ConcurrentModificationException
	at java.util.LinkedList$LLSpliterator.forEachRemaining(LinkedList.java:1239)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
	at ai.rapids.cudf.MemoryCleaner.stringJoin(MemoryCleaner.java:271)
	at ai.rapids.cudf.MemoryCleaner.access$200(MemoryCleaner.java:59)
	at ai.rapids.cudf.MemoryCleaner$Cleaner.logRefCountDebug(MemoryCleaner.java:94)
	at ai.rapids.cudf.ColumnVector$OffHeapState.cleanImpl(ColumnVector.java:3468)
	at ai.rapids.cudf.MemoryCleaner$Cleaner.clean(MemoryCleaner.java:104)
	at ai.rapids.cudf.MemoryCleaner$CleanerWeakReference.clean(MemoryCleaner.java:150)
	at ai.rapids.cudf.MemoryCleaner.lambda$static$1(MemoryCleaner.java:213)
	at java.lang.Thread.run(Thread.java:748)

Steps/Code to reproduce bug
mvn clean verify

Expected behavior
We should not see this error.

Environment details (please complete the following information)
Running on Ubuntu desktop

Additional context
N/A

[abellina]

This one is a duplicate of #1128