Fix flaky assertion bound in testThreadSafetyBruteForce

Local compaction depends on completion order and timing. Under certain cases
node count can reach or exceed `sqrt(concurrency)` before the final compaction
is triggered. The test for intermediate state was failing fairly often in CI.
This commit updates the test for intermediate state to simply be less than
`concurrency`. This should satisfy the intent of the test, with the added
security of the rest of the test asserting the finalized state is less than 2
nodes.

Author: donoghuc

src/test/java/org/logstash/plugins/inputs/http/util/ExecutionObserverTest.java

@@ -194,7 +194,7 @@ void testThreadSafetyBruteForce() {
             // without queries, we may have some compaction so we shouldn't be too strict
             final ExecutionObserver.Stats preCompactionStats = observer.stats();
             assertThat(preCompactionStats.executing, is(0));
-            assertThat(preCompactionStats.nodes, is(both(greaterThan(0)).and(lessThan((int) Math.sqrt(concurrency)))));
+            assertThat(preCompactionStats.nodes, is(both(greaterThan(0)).and(lessThan(concurrency))));
 
             // query triggers tail compaction, leaving 2 or fewer nodes.
             assertThat(observer.anyExecuting(), is(false));