Fixup BWC after backport of #92259 (#92280)

Adjusts the BWC version for the wire protocol and re-enables the BWC
tests.

build.gradle

@@ -137,9 +137,9 @@ 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/92277"
+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")

server/src/main/java/org/elasticsearch/cluster/coordination/PublicationTransportHandler.java

@@ -86,7 +86,7 @@ public class PublicationTransportHandler {
         TransportRequestOptions.Type.STATE
     );
 
-    public static final Version INCLUDES_LAST_COMMITTED_DATA_VERSION = Version.V_8_7_0;
+    public static final Version INCLUDES_LAST_COMMITTED_DATA_VERSION = Version.V_8_6_0;
 
     private final SerializationStatsTracker serializationStatsTracker = new SerializationStatsTracker();