QueryBackPressureTest regularly times out on GHA

## Flaky Test

* **Test Name:** org.janusgraph.diskstorage.util.backpressure.QueryBackPressureTest
* **Link:** https://github.com/JanusGraph/janusgraph/blob/e95578388919af6749b6a5e81f850de08c846b2d/janusgraph-core/src/test/java/org/janusgraph/diskstorage/util/backpressure/QueryBackPressureTest.java#L27
* **Branch:** `v1.0`
* **Notes:** There is no test failure, but the tests don't terminate. GH Action instead cancels the run after 6h. I don't know which test in this class is responsible for the problem or why this started becoming a problem only recently since the test class hasn't been changed since its addition in May 2023.

cc @porunov

### Stack Trace

```
[INFO] Running org.janusgraph.diskstorage.util.CompletableFutureUtilTest
[INFO] Tests run: 8, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.136 s - in org.janusgraph.diskstorage.util.CompletableFutureUtilTest
[INFO] Running org.janusgraph.diskstorage.util.backpressure.QueryBackPressureTest
Error: The operation was canceled.
```

Start with janusgraph-core/src/test/java/org/janusgraph/diskstorage/util/backpressure/QueryBackPressureTest.java and run the class in the v1.0 branch. Investigate which test or operation fails to terminate and verify the behavior in GitHub Actions. Done means the class completes reliably without the six-hour cancellation.

Written by the indexing model from the issue text.