Update serialization version after backport

Author: polyfractal

server/src/main/java/org/elasticsearch/search/aggregations/metrics/AbstractPercentilesAggregationBuilder.java

@@ -144,7 +144,7 @@ public static <T extends AbstractPercentilesAggregationBuilder<T>> ConstructingO
         super(in);
         values = in.readDoubleArray();
         keyed = in.readBoolean();
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_8_0)) {
             percentilesConfig
                 = (PercentilesConfig) in.readOptionalWriteable((Reader<Writeable>) PercentilesConfig::fromStream);
         } else {
@@ -159,7 +159,7 @@ public static <T extends AbstractPercentilesAggregationBuilder<T>> ConstructingO
     protected void innerWriteTo(StreamOutput out) throws IOException {
         out.writeDoubleArray(values);
         out.writeBoolean(keyed);
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_8_0)) {
             out.writeOptionalWriteable(percentilesConfig);
         } else {
             // Legacy method serialized both SigFigs and compression, even though we only need one.  So we need