Update version serialization for CCR backport and re-enable BWC tests (#88998)

Updates versions for backport (#88995) of original fix (#88875)

Relates to #88997

build.gradle

@@ -136,9 +136,9 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
+boolean bwc_tests_enabled = true
 // place a PR link here when committing bwc changes:
-String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/88995"
+String bwc_tests_disabled_issue = ""
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {
     throw new GradleException("bwc_tests_disabled_issue must be set when bwc_tests_enabled == false")

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/action/PutFollowAction.java

@@ -198,7 +198,7 @@ public final class PutFollowAction extends ActionType<PutFollowAction.Response>
             }
             this.parameters = new FollowParameters(in);
             waitForActiveShards(ActiveShardCount.readFrom(in));
-            if (in.getVersion().onOrAfter(Version.V_8_5_0)) {
+            if (in.getVersion().onOrAfter(Version.V_8_4_0)) {
                 this.dataStreamName = in.readOptionalString();
             }
         }
@@ -214,7 +214,7 @@ public final class PutFollowAction extends ActionType<PutFollowAction.Response>
             }
             parameters.writeTo(out);
             waitForActiveShards.writeTo(out);
-            if (out.getVersion().onOrAfter(Version.V_8_5_0)) {
+            if (out.getVersion().onOrAfter(Version.V_8_4_0)) {
                 out.writeOptionalString(this.dataStreamName);
             }
         }