Adjust serialization ver. after backport of #77151 (#77394)

This commit adjusts the serialization version and re-enables BWC tests
following the backport of #77151.

Author: gwbrown

build.gradle

@@ -138,9 +138,9 @@ 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/77278"
+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

server/src/main/java/org/elasticsearch/cluster/metadata/SingleNodeShutdownMetadata.java

@@ -35,7 +35,7 @@ public class SingleNodeShutdownMetadata extends AbstractDiffable<SingleNodeShutd
         ToXContentObject,
         Diffable<SingleNodeShutdownMetadata> {
 
-    public static final Version REPLACE_SHUTDOWN_TYPE_ADDED_VERSION = Version.V_8_0_0;
+    public static final Version REPLACE_SHUTDOWN_TYPE_ADDED_VERSION = Version.V_7_16_0;
 
     public static final ParseField NODE_ID_FIELD = new ParseField("node_id");
     public static final ParseField TYPE_FIELD = new ParseField("type");