Only check non-negative stats for active, current and queue

In SimpleThreadPoolIT, stats are gathered for each threadpool being
checked, then measurements are collected. Some stats may go up or down
depending on other background tasks outside the test. This commit
adjusts the check for those stats to only check collecting non-negative
values.

closes elastic#108320

muted-tests.yml

@@ -144,9 +144,6 @@ tests:
 - class: org.elasticsearch.xpack.shutdown.NodeShutdownIT
   method: testAllocationPreventedForRemoval
   issue: https://github.com/elastic/elasticsearch/issues/116363
-- class: org.elasticsearch.threadpool.SimpleThreadPoolIT
-  method: testThreadPoolMetrics
-  issue: https://github.com/elastic/elasticsearch/issues/108320
 - class: org.elasticsearch.xpack.downsample.ILMDownsampleDisruptionIT
   method: testILMDownsampleRollingRestart
   issue: https://github.com/elastic/elasticsearch/issues/114233

server/src/internalClusterTest/java/org/elasticsearch/threadpool/SimpleThreadPoolIT.java

@@ -167,10 +167,10 @@ public void testThreadPoolMetrics() throws Exception {
         tps[0].forEach(stats -> {
             Map<String, Long> threadPoolStats = List.of(
                 Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_COMPLETED, stats.completed()),
-                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_ACTIVE, (long) stats.active()),
-                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_CURRENT, (long) stats.threads()),
+                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_ACTIVE, 0L),
+                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_CURRENT, 0L),
                 Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_LARGEST, (long) stats.largest()),
-                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_QUEUE, (long) stats.queue())
+                Map.entry(ThreadPool.THREAD_POOL_METRIC_NAME_QUEUE, 0L)
             ).stream().collect(toUnmodifiableSortedMap(e -> stats.name() + e.getKey(), Entry::getValue));
 
             Function<String, List<Long>> measurementExtractor = name -> {