Reenable BwC Tests After #49976 (#49978)

With #49976 merged we can reenable BwC tests.

build.gradle

@@ -205,8 +205,8 @@ task verifyVersions {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/49976" /* place a PR link here when committing bwc changes */
+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/cluster/metadata/RepositoryMetaData.java

@@ -32,7 +32,7 @@ import java.util.Objects;
  */
 public class RepositoryMetaData {
 
-    public static final Version REPO_GEN_IN_CS_VERSION = Version.V_8_0_0;
+    public static final Version REPO_GEN_IN_CS_VERSION = Version.V_7_6_0;
 
     private final String name;
     private final String type;