test: use concurrent queue to avoid race condition

[mjsax]

Description

What behavior do you want to change, why, how does your patch achieve the changes?

Testing done

Describe the testing strategy. Unit and integration tests are expected for any behavior changes.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[lct45]

LGTM @mjsax, thanks for the quick fix

[vvcephei]

Thanks, @mjsax !

It seems worthwhile to point out that this was in response to a test failure:

[2022-03-10T05:51:51.892Z] [ERROR] Tests run: 8, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 203.505 s <<< FAILURE! - in io.confluent.ksql.integration.SecureIntegrationTest
[2022-03-10T05:51:51.892Z] [ERROR] io.confluent.ksql.integration.SecureIntegrationTest.shouldClassifyGroupAuthorizationExceptionAsUserError  Time elapsed: 0.511 s  <<< ERROR!
[2022-03-10T05:51:51.892Z] java.lang.ArrayIndexOutOfBoundsException
[2022-03-10T05:51:51.892Z] 	at io.confluent.ksql.integration.SecureIntegrationTest.lambda$assertQueryFailsWithUserError$5(SecureIntegrationTest.java:517)
[2022-03-10T05:51:51.892Z] 	at io.confluent.ksql.integration.SecureIntegrationTest.assertQueryFailsWithUserError(SecureIntegrationTest.java:515)
[2022-03-10T05:51:51.892Z] 	at io.confluent.ksql.integration.SecureIntegrationTest.shouldClassifyGroupAuthorizationExceptionAsUserError(SecureIntegrationTest.java:362)

While the stack trace is incomplete, digging through the Guava code indicates that the ArrayIndexOutOfBounds exception was probably thrown from the EvictingQueue due to a multithreaded race condition in toArray. Wrapping it should prevent any such bugs.

I'm not sure whether it matters, but it seems like this PR should be a fix instead of a test. I think the test was revealing a real bug in production code.