Reenable bwc and update version checks after backporting #70107 (#70574)

build.gradle

@@ -189,9 +189,9 @@ 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/70107"
+String bwc_tests_disabled_issue = ""
 /*
  * FIPS 140-2 behavior was fixed in 7.11.0. Before that there is no way to run elasticsearch in a
  * JVM that is properly configured to be in fips mode with BCFIPS. For now we need to disable

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/IndexLifecycleExplainResponse.java

@@ -209,7 +209,7 @@ public class IndexLifecycleExplainResponse implements ToXContentObject, Writeabl
                 repositoryName = null;
                 snapshotName = null;
             }
-            if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+            if (in.getVersion().onOrAfter(Version.V_7_13_0)) {
                 shrinkIndexName = in.readOptionalString();
             } else {
                 shrinkIndexName = null;
@@ -258,7 +258,7 @@ public class IndexLifecycleExplainResponse implements ToXContentObject, Writeabl
                 out.writeOptionalString(repositoryName);
                 out.writeOptionalString(snapshotName);
             }
-            if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+            if (out.getVersion().onOrAfter(Version.V_7_13_0)) {
                 out.writeOptionalString(shrinkIndexName);
             }
         }