Mute FullClusterRestartIT#testWatcher

This test has failed due to incorrect versions on the watches, see

x-pack/qa/full-cluster-restart/src/test/java/org/elasticsearch/xpack/restart/FullClusterRestartIT.java

@@ -137,6 +137,7 @@ public class FullClusterRestartIT extends AbstractFullClusterRestartTestCase {
     }
 
     @SuppressWarnings("unchecked")
+    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/40178")
     public void testWatcher() throws Exception {
         if (isRunningAgainstOldCluster()) {
             logger.info("Adding a watch on old cluster {}", getOldClusterVersion());