Fix flaky test

The test must reset the counter baseline every time it ignores an iteration due to sleeping too much.

src/test/java/blackbox/slow/PoolIT.java

@@ -298,6 +298,7 @@ void mustGraduallyReduceAggressivenessInRepairingFailingAllocator() throws Excep
       if (elapsedMillis >= 150) {
         // Ignore outliers with very high sleep time.
         i--;
+        prev = counter.get();
         continue;
       }
       curr = counter.get();