Adjust version serialization and re-enable BWC after backport (#68781)

Now that #68762 is merged, BWC should be re-enabled.

Author: dakrone

build.gradle

@@ -169,8 +169,8 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/68762" /* place a PR link here when committing bwc changes */
+boolean bwc_tests_enabled = true
+String bwc_tests_disabled_issue = "" /* place a PR link here when committing bwc changes */
 /*
  * 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/SearchableSnapshotAction.java

@@ -101,7 +101,7 @@ public SearchableSnapshotAction(StreamInput in) throws IOException {
         } else {
             this.forceMergeIndex = true;
         }
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_12_0)) {
             this.storageType = in.readOptionalEnum(MountSearchableSnapshotRequest.Storage.class);
         } else {
             this.storageType = null;
@@ -333,7 +333,7 @@ public void writeTo(StreamOutput out) throws IOException {
         if (out.getVersion().onOrAfter(Version.V_7_10_0)) {
             out.writeBoolean(forceMergeIndex);
         }
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_12_0)) {
             out.writeOptionalEnum(storageType);
         }
     }