[TEST] enable cacheKey check in ShardSearchTransportRequestTests

Now that #20081 is merged we can check that cacheKey is consistent across equal search requests, something that wasn't true before due to ordering of map keys when using index boost.

Relates to #19986

core/src/test/java/org/elasticsearch/search/internal/ShardSearchTransportRequestTests.java

@@ -91,6 +91,7 @@ public class ShardSearchTransportRequestTests extends ESTestCase {
                 assertEquals(deserializedRequest.searchType(), shardSearchTransportRequest.searchType());
                 assertEquals(deserializedRequest.shardId(), shardSearchTransportRequest.shardId());
                 assertEquals(deserializedRequest.numberOfShards(), shardSearchTransportRequest.numberOfShards());
+                assertEquals(deserializedRequest.cacheKey(), shardSearchTransportRequest.cacheKey());
                 assertNotSame(deserializedRequest, shardSearchTransportRequest);
             }
         }