SingleProcessorTest failure

[idelpivnitskiy]

https://github.com/apple/servicetalk/actions/runs/20862371073/job/59945016811?pr=3389

> Task :servicetalk-concurrent-api:test

SingleProcessorTest > synchronousCancelStillAllowsForGC() FAILED
    org.opentest4j.AssertionFailedError: expected: <java.lang.ref.WeakReference@59d35978> but was: <null>
        at app//org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
        at app//org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
        at app//org.junit.jupiter.api.AssertEquals.failNotEqual(AssertEquals.java:197)
        at app//org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
        at app//org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
        at app//org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1145)
        at app//io.servicetalk.concurrent.api.SingleProcessorTest.synchronousCancelStillAllowsForGC(SingleProcessorTest.java:198)