fix flaky test - handle IllegalStateException and throw AssertionError to use assertbusy (#11981)

* fix flaky test - handle IllegalStateException and throw AssertionError to use assertbusy

Signed-off-by: bansvaru <bansvaru@amazon.com>

* Empty Commit to retry the build

Signed-off-by: bansvaru <bansvaru@amazon.com>

---------

Signed-off-by: bansvaru <bansvaru@amazon.com>

Author: linuxpi

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

@@ -310,10 +310,16 @@ private void validateCurrentMetadata() throws Exception {
             internalCluster().getClusterManagerName()
         );
         assertBusy(() -> {
-            ClusterMetadataManifest manifest = remoteClusterStateService.getLatestClusterMetadataManifest(
-                getClusterState().getClusterName().value(),
-                getClusterState().metadata().clusterUUID()
-            ).get();
+            ClusterMetadataManifest manifest;
+            try {
+                manifest = remoteClusterStateService.getLatestClusterMetadataManifest(
+                    getClusterState().getClusterName().value(),
+                    getClusterState().metadata().clusterUUID()
+                ).get();
+            } catch (IllegalStateException e) {
+                // AssertionError helps us use assertBusy and retry validation if failed due to a race condition.
+                throw new AssertionError("Error while validating latest cluster metadata", e);
+            }
             ClusterState clusterState = getClusterState();
             Metadata currentMetadata = clusterState.metadata();
             assertEquals(currentMetadata.indices().size(), manifest.getIndices().size());