Backport Fix RetrySearchIntegTests (elastic#122919)

Don't simultaneously restart multiple nodes in a cluster. It causes data races when
multiple primaries are trying to mark the `[[.snapshot-blob-cache][0]]` shard as stale.

Author: arteam

x-pack/plugin/searchable-snapshots/src/internalClusterTest/java/org/elasticsearch/xpack/searchablesnapshots/RetrySearchIntegTests.java

@@ -90,6 +90,7 @@ public void testSearcherId() throws Exception {
         for (String allocatedNode : allocatedNodes) {
             if (randomBoolean()) {
                 internalCluster().restartNode(allocatedNode);
+                ensureGreen(indexName);
             }
         }
         ensureGreen(indexName);
@@ -151,6 +152,7 @@ public void testRetryPointInTime() throws Exception {
             final Set<String> allocatedNodes = internalCluster().nodesInclude(indexName);
             for (String allocatedNode : allocatedNodes) {
                 internalCluster().restartNode(allocatedNode);
+                ensureGreen(indexName);
             }
             ensureGreen(indexName);
             assertNoFailuresAndResponse(