Fix compilation issue for PR opensearch-project#17535 during backport (opensearch-project#17546)

Signed-off-by: Ashish Singh <ssashish@amazon.com>

Author: ashking94

server/src/internalClusterTest/java/org/opensearch/remotestore/RemoteStoreStatsIT.java

@@ -291,16 +291,16 @@ public void testDownloadStatsCorrectnessSinglePrimarySingleReplica() throws Exce
                 // Existing validation logic
                 List<RemoteStoreStats> primaryStatsList = Arrays.stream(response.getRemoteStoreStats())
                     .filter(remoteStoreStats -> remoteStoreStats.getShardRouting().primary())
-                    .toList();
+                    .collect(Collectors.toList());
                 assertEquals(1, primaryStatsList.size());
 
                 List<RemoteStoreStats> replicaStatsList = Arrays.stream(response.getRemoteStoreStats())
                     .filter(remoteStoreStats -> !remoteStoreStats.getShardRouting().primary())
-                    .toList();
+                    .collect(Collectors.toList());
                 assertEquals(1, replicaStatsList.size());
 
-                RemoteSegmentTransferTracker.Stats primaryStats = primaryStatsList.getFirst().getSegmentStats();
-                RemoteSegmentTransferTracker.Stats replicaStats = replicaStatsList.getFirst().getSegmentStats();
+                RemoteSegmentTransferTracker.Stats primaryStats = primaryStatsList.get(0).getSegmentStats();
+                RemoteSegmentTransferTracker.Stats replicaStats = replicaStatsList.get(0).getSegmentStats();
 
                 // Existing assertions
                 assertTrue(primaryStats.totalUploadsStarted > 0);
@@ -409,15 +409,15 @@ private void validateZeroStatePrimaryStats(RemoteSegmentTransferTracker.Stats pr
     private void validateZeroStateReplicaStats(RemoteStoreStatsResponse zeroStateResponse, boolean multipleShardsExpected) {
         List<RemoteStoreStats> zeroStateReplicaStats = Arrays.stream(zeroStateResponse.getRemoteStoreStats())
             .filter(remoteStoreStats -> !remoteStoreStats.getShardRouting().primary())
-            .toList();
+            .collect(Collectors.toList());
 
         if (multipleShardsExpected) {
             zeroStateReplicaStats.forEach(stats -> {
                 assertEquals(0, stats.getSegmentStats().directoryFileTransferTrackerStats.transferredBytesStarted);
                 assertEquals(0, stats.getSegmentStats().directoryFileTransferTrackerStats.transferredBytesSucceeded);
             });
         } else {
-            RemoteSegmentTransferTracker.Stats replicaStats = zeroStateReplicaStats.getFirst().getSegmentStats();
+            RemoteSegmentTransferTracker.Stats replicaStats = zeroStateReplicaStats.get(0).getSegmentStats();
             assertEquals(0, replicaStats.directoryFileTransferTrackerStats.transferredBytesStarted);
             assertEquals(0, replicaStats.directoryFileTransferTrackerStats.transferredBytesSucceeded);
         }
@@ -442,8 +442,8 @@ private SetOnce<RemoteSegmentTransferTracker.Stats> prepareZeroStateStats(
 
             RemoteSegmentTransferTracker.Stats primaryStats = Arrays.stream(zeroStateResponse.getRemoteStoreStats())
                 .filter(remoteStoreStats -> remoteStoreStats.getShardRouting().primary())
-                .toList()
-                .getFirst()
+                .collect(Collectors.toList())
+                .get(0)
                 .getSegmentStats();
 
             validateZeroStatePrimaryStats(primaryStats);