Reenable bwc tests after backport

Now that elastic#64374 has been backported to 7.x we can run the bwc tests
again without wire incompatibilities.

build.gradle

@@ -175,8 +175,8 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https:/elastic/elasticsearch/pull/64374" /* 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")