Adjust serialization versions after backport

 Relates #29533

Author: jimczi

server/src/main/java/org/elasticsearch/search/internal/ShardSearchLocalRequest.java

@@ -235,7 +235,7 @@ protected void innerReadFrom(StreamInput in) throws IOException {
         if (in.getVersion().onOrAfter(Version.V_6_3_0)) {
             allowPartialSearchResults = in.readOptionalBoolean();
         }
-        if (in.getVersion().onOrAfter(Version.V_7_0_0_alpha1)) {
+        if (in.getVersion().onOrAfter(Version.V_6_4_0)) {
             indexRoutings = in.readStringArray();
             preference = in.readOptionalString();
         } else {
@@ -268,7 +268,7 @@ protected void innerWriteTo(StreamOutput out, boolean asKey) throws IOException
             out.writeOptionalBoolean(allowPartialSearchResults);
         }
         if (asKey == false) {
-            if (out.getVersion().onOrAfter(Version.V_7_0_0_alpha1)) {
+            if (out.getVersion().onOrAfter(Version.V_6_4_0)) {
                 out.writeStringArray(indexRoutings);
                 out.writeOptionalString(preference);
             }

server/src/main/java/org/elasticsearch/search/slice/SliceBuilder.java

@@ -225,7 +225,7 @@ public Query toFilter(ClusterService clusterService, ShardSearchRequest request,
 
         int shardId = request.shardId().id();
         int numShards = context.getIndexSettings().getNumberOfShards();
-        if (minNodeVersion.onOrAfter(Version.V_7_0_0_alpha1) &&
+        if (minNodeVersion.onOrAfter(Version.V_6_4_0) &&
                 (request.preference() != null || request.indexRoutings().length > 0)) {
             GroupShardsIterator<ShardIterator> group = buildShardIterator(clusterService, request);
             assert group.size() <= numShards : "index routing shards: " + group.size() +
@@ -235,7 +235,7 @@ public Query toFilter(ClusterService clusterService, ShardSearchRequest request,
                  * The routing of this request targets a subset of the shards of this index so we need to we retrieve
                  * the original {@link GroupShardsIterator} and compute the request shard id and number of
                  * shards from it.
-                 * This behavior has been added in {@link Version#V_7_0_0_alpha1} so if there is another node in the cluster
+                 * This behavior has been added in {@link Version#V_6_4_0} so if there is another node in the cluster
                  * with an older version we use the original shard id and number of shards in order to ensure that all
                  * slices use the same numbers.
                  */