Flaky cache expiration test: ExpirationCacheTest.testExpiration

[FlorianHockmann]

Flaky Test

I saw the test fail already for two Dependabot PRs (both targeted on master) but it worked when I ran the test locally and also when I restarted the GH action.

• Test Name: ExpirationCacheTest.testExpiration
• Link: https://github.com/JanusGraph/janusgraph/blob/a60e92815b3a51a4cc020a7c7cb2bce9f414887a/janusgraph-test/src/test/java/org/janusgraph/diskstorage/cache/ExpirationCacheTest.java#L57
• Branch: master
• Notes: I'll create PR to mark it as flaky.

Stack Trace

Error:  Failures: 
Error:    ExpirationCacheTest.testExpiration:58->testExpiration:86->verifyResults:151 expected: <6> but was: <5>