Enable BWC after backport recovering leases (#38485)

This commit enables the BWC tests after backporting recovery of retention
leases during peer recovery.

build.gradle

@@ -159,8 +159,8 @@ task verifyVersions {
  * the enabled state of every bwc task. It should be set back to true
  * after the backport of the backcompat code is complete.
  */
-final boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/38435" /* place a PR link here when committing bwc changes */
+final 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/indices/recovery/RecoveryTranslogOperationsRequest.java

@@ -108,7 +108,7 @@ public class RecoveryTranslogOperationsRequest extends TransportRequest {
             // UNASSIGNED_SEQ_NO means uninitialized and replica won't enable optimization using seq_no
             maxSeqNoOfUpdatesOrDeletesOnPrimary = SequenceNumbers.UNASSIGNED_SEQ_NO;
         }
-        if (in.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_6_7_0)) {
             retentionLeases = new RetentionLeases(in);
         } else {
             retentionLeases = RetentionLeases.EMPTY;
@@ -128,7 +128,7 @@ public class RecoveryTranslogOperationsRequest extends TransportRequest {
         if (out.getVersion().onOrAfter(Version.V_6_5_0)) {
             out.writeZLong(maxSeqNoOfUpdatesOrDeletesOnPrimary);
         }
-        if (out.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_6_7_0)) {
             retentionLeases.writeTo(out);
         }
     }