[Transform] use correct version in BWC serialization test (#60500)

use correct version in BWC serialization test

fixes #60464

Author: Hendrik Muhs

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/transform/transforms/pivot/DateHistogramGroupSourceTests.java

@@ -63,7 +63,7 @@ public static DateHistogramGroupSource randomDateHistogramGroupSource(Version ve
     public void testBackwardsSerialization72() throws IOException {
         // version 7.7 introduced scripts, so test before that
         DateHistogramGroupSource groupSource = randomDateHistogramGroupSource(
-            VersionUtils.randomVersionBetween(random(), Version.V_7_3_0, Version.V_7_7_0)
+            VersionUtils.randomVersionBetween(random(), Version.V_7_3_0, Version.V_7_6_2)
         );
 
         try (BytesStreamOutput output = new BytesStreamOutput()) {