Reenable BwC Tests After #56866 (#56868)

Reenable BwC tests now that #56866 is merged.

build.gradle

@@ -174,8 +174,8 @@ task verifyVersions {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/56866" /* place a PR link here when committing bwc changes */
+boolean bwc_tests_enabled = true
+final String bwc_tests_disabled_issue = "" /* place a PR link here when committing bwc changes */
 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")

server/src/main/java/org/elasticsearch/action/bulk/BulkShardResponse.java

@@ -31,7 +31,7 @@ import java.io.IOException;
 
 public class BulkShardResponse extends ReplicationResponse implements WriteResponse {
 
-    private static final Version COMPACT_SHARD_ID_VERSION = Version.V_8_0_0;
+    private static final Version COMPACT_SHARD_ID_VERSION = Version.V_7_9_0;
 
     private final ShardId shardId;
     private final BulkItemResponse[] responses;